.lesson-page-indexed-book{--lesson-hero:var(--color-hero);--lesson-paper:var(--color-surface);--lesson-ink:var(--color-text);--lesson-navy:var(--color-primary);--lesson-muted:var(--color-text-muted);--lesson-border:var(--color-border);--lesson-paper-deep:var(--color-surface-muted);color:var(--lesson-ink)}.lesson-indexed-book{min-width:0;margin-bottom:72px;container-type:inline-size}.lesson-book-hero{isolation:isolate;border:1px solid var(--lesson-border);background:var(--lesson-hero);border-radius:4px;margin-bottom:38px;padding:clamp(42px,6vw,78px) clamp(28px,6vw,72px);position:relative;overflow:hidden}.lesson-book-hero-decoration{z-index:-1;pointer-events:none;opacity:.45;background:radial-gradient(circle at 88% 18%, color-mix(in srgb, var(--lesson-paper) 48%, transparent) 0 7%, transparent 26%), radial-gradient(circle at 8% 88%, color-mix(in srgb, var(--lesson-navy) 7%, transparent) 0 9%, transparent 29%), repeating-linear-gradient(0deg, transparent 0 34px, color-mix(in srgb, var(--lesson-ink) 3%, transparent) 34px 35px);position:absolute;inset:0}.lesson-book-hero-content{z-index:1;max-width:930px;position:relative}.lesson-book-hero .breadcrumbs{color:var(--lesson-muted);margin:0 0 clamp(40px,6vw,72px)}.lesson-book-hero .breadcrumbs a,.lesson-book-hero .breadcrumbs span[aria-current=page]{color:var(--lesson-ink)}.lesson-book-category{color:var(--lesson-navy);letter-spacing:.13em;text-transform:uppercase;margin:0 0 14px;font-size:12px;font-weight:800}.lesson-book-hero h1{max-width:900px;color:var(--lesson-ink);letter-spacing:-.035em;overflow-wrap:anywhere;margin:0;font-family:ui-serif,Georgia,Cambria,Times New Roman,serif;font-size:clamp(44px,6.4vw,76px);font-weight:700;line-height:1.01}.lesson-book-description{max-width:720px;color:var(--lesson-muted);margin:24px 0 0;font-size:clamp(17px,2vw,20px);line-height:1.6}.lesson-book-table-of-contents{border:1px solid var(--lesson-border);background:var(--lesson-paper-deep);border-radius:3px;margin:0 0 22px;padding:18px 22px}.lesson-book-table-of-contents>p{color:var(--lesson-muted);letter-spacing:.12em;text-transform:uppercase;margin:0 0 10px;font-size:11px;font-weight:800}.lesson-book-table-of-contents ol{flex-wrap:wrap;gap:8px 18px;margin:0;padding-left:20px;display:flex}.lesson-book-table-of-contents a{color:var(--lesson-navy);overflow-wrap:anywhere;font-weight:700}.lesson-book-frame{min-width:0;position:relative}.lesson-index-navigation{overscroll-behavior-inline:contain;scrollbar-width:thin;gap:8px;min-width:0;margin-bottom:14px;display:flex;overflow-x:auto}.lesson-index-collapsed-tabs{display:contents}.lesson-index-tab{border:1px solid var(--lesson-navy);min-width:0;min-height:64px;color:var(--lesson-paper);background:var(--lesson-navy);font:inherit;text-align:center;cursor:pointer;border-radius:3px;flex:1 0 min(220px,72vw);justify-content:center;align-items:center;padding:12px 14px;font-size:14px;font-weight:750;line-height:1.25;display:flex;position:relative}.lesson-index-tab-active{border:1px solid var(--lesson-border);color:var(--lesson-ink);background:var(--lesson-paper)}.lesson-index-tab-number{color:inherit;letter-spacing:.08em;flex:none;margin-right:9px;font-size:11px;font-weight:800}.lesson-index-tab-label{overflow-wrap:anywhere;min-width:0}.lesson-screen-reader-heading{clip:rect(0 0 0 0);white-space:nowrap;border:0;width:1px;height:1px;margin:-1px;padding:0;position:absolute;overflow:hidden}.lesson-book-paper{border:1px solid var(--lesson-border);background:var(--lesson-paper);border-radius:3px;min-width:0;padding:clamp(36px,5vw,68px)}.lesson-book-paper-heading{border-bottom:1px solid var(--lesson-border);margin-bottom:clamp(42px,6vw,72px);padding-bottom:28px}.lesson-book-paper-heading>p{color:var(--lesson-muted);letter-spacing:.12em;text-transform:uppercase;margin:0 0 10px;font-size:11px;font-weight:800}.lesson-book-paper-heading h2{color:var(--lesson-ink);letter-spacing:-.025em;margin:0;font-family:ui-serif,Georgia,Cambria,Times New Roman,serif;font-size:clamp(32px,4vw,46px);line-height:1.08}.lesson-book-chapter-panel{min-width:0}.lesson-book-chapter-panel[hidden]{display:none}.lesson-page-indexed-book .lesson-step+.lesson-step{border-top-color:var(--lesson-border)}.lesson-page-indexed-book .lesson-step>h3{color:var(--lesson-ink);letter-spacing:-.015em;font-family:ui-serif,Georgia,Cambria,Times New Roman,serif;font-weight:700}.lesson-page-indexed-book .lesson-step-number,.lesson-page-indexed-book .material-type,.lesson-page-indexed-book .lesson-navigation-card>span{color:var(--lesson-navy)}.lesson-page-indexed-book .lesson-markdown,.lesson-page-indexed-book .exercise-content p,.lesson-page-indexed-book .material-content p,.lesson-page-indexed-book .lesson-next-suggestion,.lesson-page-indexed-book .lesson-asset-status{color:var(--lesson-muted)}.lesson-page-indexed-book .lesson-markdown h3,.lesson-page-indexed-book .lesson-markdown h4,.lesson-page-indexed-book .lesson-markdown h5,.lesson-page-indexed-book .lesson-markdown h6,.lesson-page-indexed-book .section-heading h2,.lesson-page-indexed-book .section-heading h3,.lesson-page-indexed-book .exercise-title h3,.lesson-page-indexed-book .material-content h3{color:var(--lesson-ink)}.lesson-page-indexed-book .lesson-markdown a,.lesson-page-indexed-book .material-content a,.lesson-page-indexed-book .pdf-panel-toolbar>a,.lesson-page-indexed-book .lesson-footer a,.lesson-page-indexed-book .empty-lesson-section a{color:var(--lesson-navy)}.lesson-page-indexed-book .lesson-thought-process li{color:var(--lesson-ink)}.lesson-page-indexed-book .lesson-thought-process li:not(:last-child):after{color:var(--lesson-muted)}.lesson-page-indexed-book .video-wrapper{border-color:var(--lesson-navy);background:var(--lesson-navy);max-width:900px;box-shadow:none;border-radius:4px}.lesson-page-indexed-book .pdf-panel{border-color:var(--lesson-border);background:var(--lesson-paper);box-shadow:none;border-radius:3px}.lesson-page-indexed-book .pdf-panel-toolbar{border-bottom-color:var(--lesson-border);background:var(--lesson-paper-deep)}.lesson-page-indexed-book .pdf-panel-identity{color:var(--lesson-muted)}.lesson-page-indexed-book .pdf-panel-dots i,.lesson-page-indexed-book .pdf-panel-dots i:first-child,.lesson-page-indexed-book .pdf-panel-dots i:nth-child(2),.lesson-page-indexed-book .pdf-panel-dots i:last-child{background:var(--lesson-muted)}.lesson-page-indexed-book .pdf-panel object{background:var(--lesson-paper-deep)}.lesson-page-indexed-book .exercise-list,.lesson-page-indexed-book .material-card,.lesson-page-indexed-book .empty-lesson-section,.lesson-page-indexed-book .lesson-navigation-card{border-color:var(--lesson-border);background:var(--lesson-paper);box-shadow:none;border-radius:3px}.lesson-page-indexed-book .exercise+.exercise{border-top-color:var(--lesson-border)}.lesson-page-indexed-book .lesson-problem-tags span{border-color:var(--lesson-border);color:var(--lesson-muted);background:var(--lesson-paper-deep)}.lesson-page-indexed-book .exercise-action a{color:var(--lesson-paper);background:var(--lesson-navy)}.lesson-page-indexed-book .exercise-action a:hover{background:var(--color-primary-hover)}.lesson-page-indexed-book .material-preview,.lesson-page-indexed-book .material-placeholder{color:var(--lesson-navy);background:var(--lesson-paper-deep)}.lesson-page-indexed-book .lesson-navigation,.lesson-page-indexed-book .lesson-footer{border-color:var(--lesson-border)}.lesson-page-indexed-book .lesson-navigation-card:hover{border-color:var(--lesson-muted);box-shadow:none}.lesson-page-indexed-book a:focus-visible,.lesson-page-indexed-book button:focus-visible,.lesson-page-indexed-book .lesson-table-scroll:focus-visible{outline:3px solid var(--color-focus);outline-offset:3px}@container (width>=820px){.lesson-book-frame{--lesson-tab-rail-width:74px;padding-right:calc(var(--lesson-tab-rail-width) + 12px)}.lesson-book-frame-single-tab{padding-right:0}.lesson-index-navigation{margin:0;display:block;position:relative;overflow:visible}.lesson-index-tab-active{text-align:left;border-bottom:0;border-radius:3px 3px 0 0;justify-content:flex-start;width:100%;min-height:72px;padding:16px 22px;display:flex}.lesson-index-collapsed-tabs{z-index:2;top:0;right:calc(-1 * (var(--lesson-tab-rail-width) + 12px));width:var(--lesson-tab-rail-width);overscroll-behavior-block:contain;scrollbar-width:thin;flex-direction:column;gap:12px;max-height:min(720px,76vh);display:flex;position:absolute;overflow-y:auto}.lesson-index-tab-collapsed{width:var(--lesson-tab-rail-width);writing-mode:vertical-rl;text-orientation:mixed;border-left-width:0;border-radius:0 3px 3px 0;flex:0 0 118px;min-height:118px;padding:12px 10px}.lesson-index-tab-collapsed .lesson-index-tab-number{display:none}.lesson-index-tab-collapsed .lesson-index-tab-label{text-align:center;white-space:normal}.lesson-book-paper{border-top-left-radius:0;min-height:650px}.lesson-index-tab-active:focus-visible,.lesson-index-tab-collapsed:focus-visible{z-index:3}}@media (width<=720px){.lesson-indexed-book{margin-bottom:52px}.lesson-book-hero{margin-inline:-2px;margin-bottom:24px;padding:34px 22px 38px}.lesson-book-hero .breadcrumbs{margin-bottom:38px}.lesson-book-hero h1{font-size:clamp(37px,12vw,52px)}.lesson-book-description{margin-top:18px;font-size:16px}.lesson-index-tab{min-height:52px;padding:11px 12px;font-size:13px}.lesson-book-paper{padding:34px 20px 44px}.lesson-book-paper-heading{margin-bottom:40px;padding-bottom:22px}}@media (width<=360px){.lesson-index-tab{flex-basis:min(196px,78vw);min-height:52px;font-size:12px}}@media (prefers-reduced-motion:reduce){.lesson-index-tab,.lesson-navigation-card{transition:none}}.lesson-page{width:min(1120px,100% - 64px);margin:0 auto;padding:36px 0 96px}.breadcrumbs{color:var(--color-text-muted);flex-wrap:wrap;align-items:center;gap:8px 10px;margin-bottom:58px;font-size:13px;display:flex}.breadcrumbs a{color:var(--color-primary);text-decoration:none}.breadcrumbs a:hover{text-decoration:underline}.breadcrumbs span[aria-current=page]{color:var(--color-text-muted)}.lesson-header{max-width:900px;margin-bottom:64px}.lesson-section[id],.lesson-subsection[id],.lesson-index-navigation li[id],.lesson-material-entry[id]{scroll-margin-top:24px}.lesson-header h1{letter-spacing:-.045em;overflow-wrap:anywhere;max-width:900px;margin:12px 0 0;font-size:clamp(42px,6vw,74px);line-height:1.02}.lesson-missing-header>p:not(.eyebrow){color:var(--color-text-muted);margin:22px 0;font-size:18px;line-height:1.6}.lesson-section{border-top:1px solid var(--color-border);padding:56px 0 64px;position:relative}.section-heading{margin-bottom:28px}.section-heading h2{letter-spacing:-.025em;margin:0;font-size:clamp(27px,3vw,34px);line-height:1.15}.section-heading h3{letter-spacing:-.02em;margin:0;font-size:clamp(23px,2.4vw,29px);line-height:1.2}.lesson-step+.lesson-step{border-top:1px solid var(--color-border);margin-top:64px;padding-top:56px}.lesson-step>h3{letter-spacing:-.025em;max-width:900px;margin:8px 0 30px;font-size:clamp(25px,3vw,34px);line-height:1.2}.lesson-step-number{color:var(--color-primary);letter-spacing:.1em;text-transform:uppercase;margin:0;font-size:12px;font-weight:800}.lesson-narrow-content{max-width:820px}.lesson-subsection{min-width:0;margin:34px 0}.lesson-subsection:first-child{margin-top:0}.lesson-subsection:last-child{margin-bottom:0}.lesson-subsection .section-heading{margin-bottom:20px}.lesson-thought-process{flex-wrap:wrap;gap:10px;margin:30px 0 0;padding:0;list-style:none;display:flex}.lesson-thought-process li{color:var(--color-text);align-items:center;gap:10px;font-weight:750;display:flex}.lesson-thought-process li:not(:last-child):after{color:var(--color-text-muted);content:"→"}.lesson-theory-flow{margin-top:52px}.lesson-material-entry{min-width:0}.video-wrapper{aspect-ratio:16/9;border:1px solid var(--color-primary);background:var(--color-primary);box-shadow:0 18px 45px color-mix(in srgb, var(--color-primary) 12%, transparent);border-radius:18px;position:relative;overflow:hidden}.video-wrapper iframe{border:0;width:100%;height:100%;display:block}.pdf-panel-stage{height:calc(clamp(520px,75vh,850px) + clamp(140px,18vh,220px))}.pdf-panel{border:1px solid var(--color-border);background:var(--color-surface);width:100%;height:clamp(520px,75vh,850px);min-height:0;box-shadow:0 20px 50px color-mix(in srgb, var(--color-primary) 11%, transparent);border-radius:18px;flex-direction:column;display:flex;position:sticky;top:24px;overflow:hidden}.pdf-panel-toolbar{border-bottom:1px solid var(--color-border);background:var(--color-surface-muted);flex:none;justify-content:space-between;align-items:center;gap:20px;min-height:52px;padding:10px 16px;display:flex}.pdf-panel-identity{color:var(--color-text-muted);align-items:center;gap:13px;font-size:13px;font-weight:700;display:flex}.pdf-panel-dots{gap:5px;display:flex}.pdf-panel-dots i{background:var(--color-border);border-radius:50%;width:8px;height:8px;display:block}.pdf-panel-dots i:first-child{background:#f87171}.pdf-panel-dots i:nth-child(2){background:#fbbf24}.pdf-panel-dots i:last-child{background:#4ade80}.pdf-panel-toolbar>a{color:var(--color-primary);font-size:13px;font-weight:750;text-decoration:none}.pdf-panel-toolbar>a:hover{text-decoration:underline}.pdf-panel object{background:var(--color-surface-muted);overscroll-behavior:contain;border:0;flex:auto;width:100%;min-height:0;display:block}.pdf-fallback{text-align:center;place-content:center;height:100%;padding:40px;display:grid}.pdf-fallback strong{font-size:19px}.pdf-fallback p{color:var(--color-text-muted);margin:9px 0 18px}.pdf-fallback a{color:var(--color-primary);font-weight:750}.secondary-button{border:1px solid var(--color-border);color:var(--color-text);background:var(--color-surface);border-radius:9px;padding:11px 16px;text-decoration:none;display:inline-block}.exercise-list{border:1px solid var(--color-border);background:var(--color-surface);box-shadow:0 10px 30px color-mix(in srgb, var(--color-primary) 5%, transparent);border-radius:18px;overflow:hidden}.exercise{grid-template-columns:48px minmax(0,1fr) auto;align-items:center;gap:18px;padding:24px;display:grid}.exercise+.exercise{border-top:1px solid var(--color-border)}.exercise-number{color:var(--color-text-muted);font-weight:750}.exercise-title{flex-wrap:wrap;align-items:center;gap:10px 12px;display:flex}.exercise-title h3{margin:0}.exercise-content p{color:var(--color-text-muted);margin:8px 0 0;line-height:1.55}.difficulty{background:var(--color-surface);border:1px solid;border-radius:999px;padding:4px 9px;font-size:12px;font-weight:800}.difficulty.rating-newbie{color:var(--color-rating-newbie);background:#f4f4f4}.difficulty.rating-pupil{color:var(--color-rating-pupil);background:#effbef}.difficulty.rating-specialist{color:var(--color-rating-specialist);background:#ecfbfa}.difficulty.rating-expert{color:var(--color-rating-expert);background:#f0f2ff}.difficulty.rating-candidate-master{color:var(--color-rating-candidate-master);background:#fbf0fb}.difficulty.rating-master{color:var(--color-rating-master);background:#fff7e8}.difficulty.rating-grandmaster{color:var(--color-rating-grandmaster);background:#fff0f0}.lesson-problem-tags{flex-wrap:wrap;gap:6px;margin-top:13px;display:flex}.lesson-problem-tags span{border:1px solid var(--color-border);color:var(--color-text-muted);background:var(--color-surface-muted);border-radius:6px;padding:4px 8px;font-size:11px}.exercise-action a{color:var(--color-surface);background:var(--color-primary);border-radius:8px;padding:10px 14px;font-size:13px;font-weight:750;text-decoration:none;display:inline-block}.exercise-action a:hover{background:var(--color-primary-hover)}.empty-lesson-section{border:1px solid var(--color-border);text-align:center;background:var(--color-surface);border-radius:16px;padding:48px 24px}.empty-lesson-section h3{margin:0;font-size:22px}.empty-lesson-section p{color:var(--color-text-muted);margin:10px 0 20px}.empty-lesson-section a{color:var(--color-primary);font-weight:750;text-decoration:none}.materials-grid{grid-template-columns:repeat(2,minmax(0,1fr));gap:24px;display:grid}.material-card{border:1px solid var(--color-border);background:var(--color-surface);box-shadow:0 10px 30px color-mix(in srgb, var(--color-primary) 5%, transparent);border-radius:18px;overflow:hidden}.material-preview{aspect-ratio:16/10;background:var(--color-surface-muted);overflow:hidden}.material-preview img{object-fit:contain;width:100%;height:100%;display:block}.material-placeholder{aspect-ratio:16/10;color:var(--color-primary);background:var(--color-surface-muted);place-items:center;display:grid}.material-placeholder span{letter-spacing:.08em;font-size:30px;font-weight:800}.material-content{padding:24px}.material-type{color:var(--color-primary);letter-spacing:.08em;text-transform:uppercase;font-size:11px;font-weight:750}.material-content h3{margin:8px 0}.material-content p{color:var(--color-text-muted);line-height:1.55}.material-content a{color:var(--color-primary);font-weight:750;text-decoration:none}.lesson-navigation{border-top:1px solid var(--color-border);grid-template-columns:repeat(2,minmax(0,1fr));gap:18px;padding:56px 0;display:grid}.lesson-navigation-card{border:1px solid var(--color-border);background:var(--color-surface);min-height:120px;box-shadow:0 8px 24px color-mix(in srgb, var(--color-primary) 4%, transparent);border-radius:16px;flex-direction:column;gap:9px;padding:22px 24px;text-decoration:none;transition:border-color .15s,box-shadow .15s,transform .15s;display:flex}.lesson-navigation-card:hover{border-color:var(--color-primary);box-shadow:0 14px 32px color-mix(in srgb, var(--color-primary) 10%, transparent);transform:translateY(-2px)}.lesson-navigation-card>span{color:var(--color-primary);letter-spacing:.04em;text-transform:uppercase;font-size:12px;font-weight:750}.lesson-navigation-card>strong{font-size:19px;line-height:1.35}.lesson-navigation-next{text-align:right;grid-column:2}.lesson-footer{border-top:1px solid var(--color-border);justify-content:space-between;gap:24px;padding:36px 0;display:flex}.lesson-footer a{color:var(--color-primary);font-weight:750;text-decoration:none}.lesson-footer a:hover{text-decoration:underline}.lesson-markdown{min-width:0;max-width:780px;color:var(--color-text-muted);font-size:17px;line-height:1.75}.lesson-markdown p,.lesson-markdown li,.lesson-markdown a{overflow-wrap:anywhere}.lesson-markdown>:first-child{margin-top:0}.lesson-markdown>:last-child{margin-bottom:0}.lesson-markdown h3,.lesson-markdown h4,.lesson-markdown h5,.lesson-markdown h6{color:var(--color-text);line-height:1.25}.lesson-markdown h3{margin:38px 0 14px;font-size:25px}.lesson-markdown h4{margin:30px 0 12px;font-size:21px}.lesson-markdown h5,.lesson-markdown h6{margin:25px 0 10px;font-size:18px}.lesson-markdown a{color:var(--color-primary);font-weight:650}.lesson-markdown code:not(.lesson-code-block code){background:var(--color-surface-muted);border-radius:5px;padding:2px 5px;font-size:.9em}.lesson-table-scroll{max-width:100%;margin:24px 0;overflow-x:auto}.lesson-markdown table{border-collapse:collapse;min-width:760px;font-size:15px}.lesson-markdown th,.lesson-markdown td{border:1px solid var(--color-border);text-align:left;padding:10px 12px}.lesson-markdown th{background:var(--color-surface-muted)}.lesson-markdown .katex-display{max-width:100%;padding-block:4px;overflow:auto hidden}.lesson-objectives ul,.lesson-recap ul{gap:12px;max-width:780px;margin:0;padding-left:24px;line-height:1.6;display:grid}.lesson-callout{border:1px solid var(--color-border);background:var(--color-surface);border-left-width:5px;border-radius:14px;margin:28px 0;padding:30px}.lesson-callout-tip{background:#f2fbf4;border-left-color:#16a34a}.lesson-callout-warning{background:#fff8eb;border-left-color:#d97706}.lesson-callout-important{background:#fff5f5;border-left-color:#dc2626}.lesson-callout-note{border-left-color:var(--color-primary);background:var(--color-surface-muted)}.lesson-callout .section-heading{margin-bottom:16px}.lesson-pitfall-list{gap:14px;max-width:820px;display:grid}.lesson-pitfall-list article{border:1px solid var(--color-border);background:var(--color-surface);border-radius:12px;padding:20px 22px}.lesson-pitfall-list h3{margin:0 0 7px;font-size:18px}.lesson-pitfall-list p{color:var(--color-text-muted);overflow-wrap:anywhere;margin:0;line-height:1.55}.lesson-next-suggestion{max-width:780px;color:var(--color-text-muted);margin-top:24px}.lesson-code-block{border:1px solid var(--color-border);background:var(--color-surface);border-radius:14px;min-width:0;max-width:100%;margin:22px 0;overflow:hidden}.lesson-code-toolbar{border-bottom:1px solid var(--color-border);min-height:44px;color:var(--color-text-muted);background:var(--color-surface-muted);justify-content:space-between;align-items:center;gap:16px;padding:7px 12px 7px 16px;font-size:12px;font-weight:750;display:flex}.lesson-code-toolbar button{border:1px solid var(--color-border);color:var(--color-text);background:var(--color-surface);cursor:pointer;border-radius:7px;padding:7px 10px}.lesson-code-block pre{font-size:14px;line-height:1.6;overflow-x:auto;background:0 0!important;margin:0!important;padding:20px!important}.lesson-code-line{min-height:1.6em;display:block}.lesson-code-variant{color:var(--color-text-muted);margin:-14px 0 18px}.lesson-complexity{flex-wrap:wrap;gap:16px;max-width:780px;margin:20px 0;display:flex}.lesson-complexity>div{border:1px solid var(--color-border);background:var(--color-surface);border-radius:10px;min-width:210px;padding:14px 16px}.lesson-complexity dt{color:var(--color-text-muted);font-size:12px;font-weight:700}.lesson-complexity dd{margin:5px 0 0;font-weight:750}.lesson-asset-status{color:var(--color-text-muted)}.lesson-asset-error{color:#991b1b;overflow-wrap:anywhere;background:#fff5f5;border:1px solid #f1b8b8;border-radius:10px;max-width:780px;padding:18px}.lesson-asset-error p{margin:6px 0 0}.lesson-page a:focus-visible{outline:3px solid var(--color-focus);outline-offset:3px;border-radius:4px}.lesson-page button:focus-visible,.lesson-table-scroll:focus-visible{outline:3px solid var(--color-focus);outline-offset:3px}@media (width<=900px){.lesson-page{width:min(100% - 48px,1120px);padding-top:32px}.pdf-panel{height:clamp(500px,72vh,760px);position:static}.pdf-panel-stage{height:auto}}@media (width<=720px){.lesson-page{width:min(100% - 28px,1120px);padding:24px 0 64px}.breadcrumbs{margin-bottom:42px;font-size:12px}.lesson-header{margin-bottom:48px}.lesson-header h1{font-size:clamp(34px,10vw,52px)}.lesson-section{padding:42px 0 48px}.lesson-section.lesson-callout{padding:24px 20px}.section-heading{margin-bottom:22px}.lesson-step+.lesson-step{margin-top:44px;padding-top:40px}.lesson-step>h3{margin-bottom:24px}.lesson-subsection{margin:28px 0}.lesson-theory-flow{margin-top:40px}.lesson-thought-process{flex-direction:column;align-items:flex-start}.lesson-thought-process li:not(:last-child):after{content:"↓"}.video-wrapper,.pdf-panel,.exercise-list,.material-card{border-radius:14px}.pdf-panel{height:clamp(440px,68vh,650px)}.pdf-panel-toolbar{flex-direction:column;align-items:flex-start;gap:7px;padding:11px 14px}.pdf-panel-identity{display:none}.exercise{grid-template-columns:32px minmax(0,1fr);gap:14px;padding:20px 16px}.exercise-action{grid-column:2}.materials-grid{grid-template-columns:1fr}.lesson-navigation{grid-template-columns:1fr;padding:44px 0}.lesson-navigation-next{text-align:left;grid-column:1}.lesson-footer{flex-direction:column;align-items:flex-start}}.problems-page{width:min(1180px,100%);margin:0 auto;padding:54px 48px 90px}.problems-header{border:1px solid var(--color-border);background:var(--color-hero);border-radius:4px;justify-content:space-between;align-items:end;gap:44px;padding:36px;display:flex}.problems-header>div:first-child{max-width:760px}.problems-eyebrow{color:var(--color-primary);letter-spacing:.11em;text-transform:uppercase;margin:0;font-size:12px;font-weight:750}.problems-header h1{letter-spacing:-.05em;margin:10px 0 20px;font-size:clamp(44px,6vw,76px);line-height:.98}.problems-header>div:first-child>p:last-child{color:var(--color-text-muted);margin:0;font-size:18px;line-height:1.6}.problems-summary{flex-direction:column;align-items:end;padding-bottom:5px;display:flex}.problems-summary strong{color:var(--color-primary);font-size:34px}.problems-summary span{color:var(--color-text-muted);font-size:13px}.problem-filters{border:1px solid var(--color-border);background:var(--color-surface);border-radius:14px;grid-template-columns:minmax(260px,1fr) 250px 210px;gap:15px;margin-top:28px;padding:20px;display:grid}.problem-filters label{flex-direction:column;gap:8px;display:flex}.problem-filters label>span{color:var(--color-text-muted);font-size:12px;font-weight:700}.problem-filters input,.problem-filters select{border:1px solid var(--color-border);width:100%;min-height:43px;color:var(--color-text);background:var(--color-surface);border-radius:8px;padding:0 12px}.problem-filters input:focus-visible,.problem-filters select:focus-visible{border-color:var(--color-primary);outline-color:var(--color-focus)}.problems-results{padding-top:44px}.results-heading{justify-content:space-between;align-items:center;gap:20px;margin-bottom:17px;display:flex}.results-heading h2{margin:0;font-size:29px}.results-heading span{color:var(--color-text-muted);font-size:13px}.problems-table-wrap{border:1px solid var(--color-border);background:var(--color-surface);border-radius:14px;overflow-x:auto}.problems-table{border-collapse:collapse;width:100%;min-width:820px}.problems-table th,.problems-table td{border-bottom:1px solid var(--color-border);text-align:left;vertical-align:middle;padding:16px 14px}.problems-table tr:last-child td{border-bottom:0}.problems-table th{color:var(--color-text-muted);background:var(--color-surface-muted);letter-spacing:.025em;font-size:12px;font-weight:700}.problems-table tbody tr:hover{background:color-mix(in srgb, var(--color-surface-muted) 62%, var(--color-surface))}.problem-index{width:48px;color:var(--color-text-muted);font-weight:750}.problem-name{min-width:270px}.problem-name strong{font-size:15px;display:block}.problem-name span{max-width:440px;color:var(--color-text-muted);margin-top:5px;font-size:12px;line-height:1.45;display:block}.problem-tags{flex-wrap:wrap;gap:6px;min-width:180px;display:flex}.problem-tags button{border:1px solid var(--color-border);color:var(--color-text-muted);background:var(--color-surface-muted);cursor:pointer;border-radius:999px;padding:4px 8px;font-size:11px}.problem-tags button:hover{border-color:var(--color-primary);color:var(--color-primary);background:var(--color-hero)}.problem-rating{font-weight:800}.rating-newbie{color:var(--color-rating-newbie)}.rating-pupil{color:var(--color-rating-pupil)}.rating-specialist{color:var(--color-rating-specialist)}.rating-expert{color:var(--color-rating-expert)}.rating-candidate-master{color:var(--color-rating-candidate-master)}.rating-master{color:var(--color-rating-master)}.rating-grandmaster{color:var(--color-rating-grandmaster)}.problem-link{color:var(--color-primary);text-underline-offset:2px;font-weight:700;text-decoration:underline}.problem-link:hover{text-decoration:underline}.problem-coming-soon{color:var(--color-text-muted);font-size:12px}.empty-problems{border:1px solid var(--color-border);text-align:center;background:var(--color-surface);border-radius:14px;padding:66px 24px}.empty-problems h3{margin:0;font-size:22px}.empty-problems p{color:var(--color-text-muted);margin:9px 0 20px}.empty-problems button{color:var(--color-surface);background:var(--color-primary);cursor:pointer;border:0;border-radius:8px;padding:10px 15px;font-weight:700}.empty-problems button:hover{background:var(--color-primary-hover)}@media (width<=1100px){.problem-filters{grid-template-columns:1fr}}@media (width<=900px){.problems-page{padding:42px 28px 76px}}@media (width<=650px){.problems-page{padding:34px 18px 66px}.problems-header{flex-direction:column;align-items:flex-start}.problems-summary{align-items:flex-start}}.sr-only{clip:rect(0, 0, 0, 0);white-space:nowrap;border:0;width:1px;height:1px;margin:-1px;padding:0;position:absolute;overflow:hidden}.application-shell{background:var(--color-page);grid-template-columns:250px minmax(0,1fr);min-height:100vh;display:grid}.application-content{min-width:0}.sidebar{border-right:1px solid var(--color-border);background:var(--color-surface);scrollbar-width:thin;scrollbar-color:var(--color-border) transparent;height:100vh;padding:22px 14px 42px;position:sticky;top:0;overflow-y:auto}.sidebar-brand{border-bottom:1px solid var(--color-border);align-items:center;gap:10px;padding:4px 7px 20px;text-decoration:none;display:flex}.sidebar-brand-mark{width:36px;height:36px;color:var(--color-surface);background:var(--color-primary);border-radius:9px;flex-shrink:0;place-items:center;font-size:13px;font-weight:800;display:grid}.sidebar-brand>span:last-child{flex-direction:column;min-width:0;display:flex}.sidebar-brand strong{font-size:14px}.sidebar-brand small{color:var(--color-text-muted);margin-top:2px;font-size:10px}.primary-navigation{align-content:start;gap:5px;min-width:0;padding:18px 0 4px;display:grid}.primary-nav-link{min-height:44px;color:var(--color-text);border-radius:8px;justify-content:space-between;align-items:center;gap:12px;padding:10px 11px;font-size:14px;font-weight:700;text-decoration:none;transition:color .15s,background-color .15s;display:flex}.primary-nav-link:hover{color:var(--color-primary);background:var(--color-surface-muted)}.primary-nav-link.is-active{color:var(--color-surface);background:var(--color-primary)}.primary-nav-link>span:last-child{font-size:18px;font-weight:400}.sidebar-library-section{min-width:0}.sidebar-library-row{grid-template-columns:minmax(0,1fr) 44px;min-width:0;display:grid}.sidebar-library-link{overflow-wrap:anywhere;border-radius:8px 0 0 8px;min-width:0}.sidebar-library-toggle{width:44px;min-height:44px;color:var(--color-text-muted);cursor:pointer;background:0 0;border:0;border-radius:0 8px 8px 0;place-items:center;padding:0;display:grid}.sidebar-library-toggle>span,.sidebar-chevron{font-size:18px;transition:transform .15s}.sidebar-library-toggle[aria-expanded=true]>span,.sidebar-category-toggle[aria-expanded=true] .sidebar-chevron{transform:rotate(90deg)}.sidebar-library-toggle:hover{color:var(--color-primary);background:var(--color-surface-muted)}.sidebar-library-link.is-active+.sidebar-library-toggle{color:var(--color-surface);background:var(--color-primary)}.sidebar-library-section.has-active-descendant .sidebar-library-link,.sidebar-library-section.has-active-descendant .sidebar-library-toggle{color:var(--color-primary);background:var(--color-surface-muted)}.sidebar-library-tree{border-left:1px solid var(--color-border);scrollbar-width:thin;scrollbar-color:var(--color-border) transparent;max-height:min(52vh,520px);margin:5px 0 7px 10px;padding-left:8px;overflow:hidden auto}.sidebar-lesson-category{min-width:0}.sidebar-category-toggle{width:100%;min-height:44px;color:var(--color-text-muted);cursor:pointer;text-align:left;-webkit-user-select:none;user-select:none;background:0 0;border:0;border-radius:8px;justify-content:space-between;align-items:center;gap:10px;padding:8px 8px 8px 10px;font-size:12px;font-weight:750;display:flex}.sidebar-category-toggle>span:first-child{overflow-wrap:anywhere;min-width:0}.sidebar-chevron{color:var(--color-text-muted);flex-shrink:0}.sidebar-category-toggle:hover{color:var(--color-primary);background:var(--color-surface-muted)}.sidebar-category-toggle[aria-expanded=true]{color:var(--color-primary)}.sidebar-category-lessons{gap:2px;padding:0 0 7px 12px;display:grid}.sidebar-lesson-link{min-width:0;min-height:36px;color:var(--color-text-muted);overflow-wrap:anywhere;border-radius:7px;padding:9px 8px 9px 13px;font-size:13px;line-height:1.35;text-decoration:none;display:block}.sidebar-lesson-link:hover{color:var(--color-primary);background:var(--color-surface-muted)}.sidebar-lesson-link.is-active{color:var(--color-primary);background:var(--color-hero);box-shadow:inset 3px 0 0 var(--color-primary);font-weight:750}.mobile-menu-button,.sidebar-backdrop{display:none}.home-content,.paths-page{width:min(1180px,100%);margin:0 auto;padding:54px 48px 90px}.page-header{border:1px solid var(--color-border);background:var(--color-hero);border-radius:4px;justify-content:space-between;align-items:end;gap:32px;padding:36px;display:flex}.page-header>div{max-width:770px}.eyebrow,.section-kicker{color:var(--color-primary);letter-spacing:.11em;text-transform:uppercase;margin:0;font-size:12px;font-weight:750}.page-header h1{letter-spacing:-.05em;margin:10px 0 20px;font-size:clamp(44px,6vw,76px);line-height:.98}.page-header p:last-child{color:var(--color-text-muted);margin:0;font-size:18px;line-height:1.6}.global-search input{border:1px solid var(--color-border);width:250px;min-height:44px;color:var(--color-text);background:var(--color-surface);border-radius:9px;padding:0 13px}.popular-section{padding:48px 0 66px}.section-title-row{justify-content:space-between;align-items:end;gap:24px;margin-bottom:28px;display:flex}.section-title-row h2,.home-path-preview h2{letter-spacing:-.035em;margin:7px 0 0;font-size:clamp(29px,4vw,42px);line-height:1.1}.lesson-count{color:var(--color-text-muted);padding-bottom:5px;font-size:14px}.popular-grid{border:1px solid var(--color-border);background:var(--color-surface);border-radius:16px;grid-template-columns:repeat(2,minmax(0,1fr));display:grid;overflow:hidden}.popular-topic-card{min-width:0;min-height:240px;color:var(--color-text);background:var(--color-surface);padding:27px;text-decoration:none;transition:background-color .15s,box-shadow .15s}.popular-topic-card:nth-child(odd){border-right:1px solid var(--color-border)}.popular-topic-card:nth-child(n+3){border-top:1px solid var(--color-border)}a.popular-topic-card{cursor:pointer}a.popular-topic-card:hover,a.popular-topic-card:focus-visible,a.popular-topic-card:focus-within{z-index:1;background:var(--color-surface-muted);box-shadow:inset 0 0 0 2px var(--color-primary);position:relative}.topic-card-top{justify-content:space-between;gap:20px;display:flex}.topic-category-label{color:var(--color-primary);letter-spacing:.08em;text-transform:uppercase;font-size:12px;font-weight:750}.topic-status{border:1px solid var(--color-border);color:var(--color-text-muted);background:0 0;border-radius:6px;padding:3px 7px;font-size:12px;line-height:1.2}.popular-topic-card h3{margin:30px 0 10px;font-size:26px}.popular-topic-card>p{max-width:470px;min-height:62px;color:var(--color-text-muted);margin:0;line-height:1.55}.topic-card-footer{color:var(--color-primary);justify-content:space-between;gap:18px;margin-top:24px;font-size:14px;font-weight:700;display:flex}.unavailable-card{color:var(--color-text-muted);background:var(--color-surface-unavailable);cursor:default}.unavailable-card .topic-category-label,.unavailable-card .topic-card-footer{color:var(--color-text-muted)}.empty-topics{border:1px solid var(--color-border);text-align:center;background:var(--color-surface);border-radius:16px;padding:54px 28px}.empty-topics h3{margin:0 0 8px;font-size:22px}.empty-topics p{color:var(--color-text-muted);margin:0}.home-path-preview{border-top:1px solid var(--color-border);justify-content:space-between;align-items:center;gap:32px;padding:54px 0;display:flex}.home-path-preview>div{max-width:690px}.home-path-preview p:last-child{color:var(--color-text-muted)}.primary-button{color:var(--color-surface);background:var(--color-primary);border-radius:9px;flex-shrink:0;padding:12px 16px;font-weight:700;text-decoration:none}.primary-button:hover{background:var(--color-primary-hover)}.paths-list{border:1px solid var(--color-border);background:var(--color-surface);border-radius:4px;margin-top:28px;padding:0 24px}.learning-path-row{border-bottom:1px solid var(--color-border);grid-template-columns:58px minmax(0,1fr) 160px;align-items:center;gap:18px;padding:25px 0;display:grid}.learning-path-row:last-child{border-bottom:0}.path-number{width:46px;height:46px;color:var(--color-primary);background:var(--color-surface-muted);border-radius:50%;place-items:center;font-weight:750;display:grid}.learning-path-row h2{margin:0 0 7px;font-size:22px}.learning-path-row p{color:var(--color-text-muted);margin:0 0 8px}.learning-path-row>div>span{color:var(--color-text-muted);font-size:13px}.path-progress>span{color:var(--color-text-muted);text-align:right;margin-bottom:8px;font-size:13px;display:block}.path-progress>div{background:var(--color-surface-muted);border-radius:99px;height:7px;overflow:hidden}.path-progress i{border-radius:inherit;background:var(--color-primary);height:100%;display:block}.not-found{min-height:100vh;padding:70px 48px}.not-found h1{font-size:48px}.not-found a{color:var(--color-primary);font-weight:700}@media (width<=900px){.application-shell{display:block}.mobile-menu-button{z-index:30;border:0;border-bottom:1px solid var(--color-border);width:100%;min-height:50px;color:var(--color-text);background:color-mix(in srgb, var(--color-surface) 95%, transparent);cursor:pointer;-webkit-backdrop-filter:blur(10px);backdrop-filter:blur(10px);align-items:center;gap:9px;padding:14px 20px;display:flex;position:sticky;top:0}.sidebar{z-index:25;width:min(330px,88vw);height:auto;box-shadow:16px 0 40px color-mix(in srgb, var(--color-primary) 15%, transparent);transition:transform .18s;position:fixed;top:50px;bottom:0;left:0;transform:translate(-105%)}.sidebar-open{transform:translate(0)}.sidebar-backdrop{z-index:20;background:color-mix(in srgb, var(--color-primary) 35%, transparent);border:0;width:100%;display:block;position:fixed;inset:50px 0 0}.home-content,.paths-page{padding:42px 28px 76px}}@media (width<=650px){.home-content,.paths-page{padding:34px 18px 66px}.page-header{flex-direction:column;align-items:stretch}.global-search input{width:100%}.popular-grid{grid-template-columns:1fr}.popular-topic-card{min-height:auto}.popular-topic-card:nth-child(odd){border-right:0}.popular-topic-card:nth-child(n+2){border-top:1px solid var(--color-border)}.popular-topic-card>p{min-height:auto}.section-title-row,.home-path-preview{flex-direction:column;align-items:flex-start}.learning-path-row{grid-template-columns:48px minmax(0,1fr)}.path-progress{grid-column:2}}:root{--color-page:#f1eee8;--color-hero:#d4ccbf;--color-surface:#fcfaf6;--color-surface-muted:#eae4da;--color-surface-unavailable:#f3f0ea;--color-primary:#282c39;--color-primary-hover:#373c4b;--color-text:#22242b;--color-text-muted:#5b5a57;--color-border:#ded8ce;--color-focus:#282c39;--color-rating-newbie:#646464;--color-rating-pupil:#006f00;--color-rating-specialist:#00766f;--color-rating-expert:#0000d6;--color-rating-candidate-master:#920092;--color-rating-master:#985000;--color-rating-grandmaster:#c40000;color:var(--color-text);background:var(--color-page);font-synthesis:none;font-family:Inter,ui-sans-serif,system-ui,-apple-system,BlinkMacSystemFont,Segoe UI,sans-serif}*{box-sizing:border-box}html,body,#root{min-width:0;min-height:100%}body{background:var(--color-page);min-height:100vh;margin:0}button,input,select,textarea{font:inherit}a{color:inherit}:where(a,button,input,select,textarea,summary):focus-visible{outline:3px solid var(--color-focus);outline-offset:3px}::selection{color:var(--color-text);background:var(--color-hero)}