:root{font-family:Inter,PingFang SC,Microsoft YaHei,system-ui,-apple-system,sans-serif;color:#172033;background:#f3f5f7;font-synthesis:none;text-rendering:optimizeLegibility;--ink: #172033;--muted: #657184;--line: #dce2e8;--surface: #ffffff;--surface-soft: #f7f9fa;--teal: #087f72;--teal-dark: #06685e;--teal-soft: #e4f5f1;--navy: #172d44;--green: #16835d;--green-soft: #e7f6ef;--amber: #a66308;--amber-soft: #fff3dc;--red: #bd3f4b;--red-soft: #ffebee}*{box-sizing:border-box}html{scroll-behavior:smooth}body{margin:0;min-width:320px;min-height:100vh;background:#f3f5f7}button,input,select{font:inherit;letter-spacing:0}button,a,select{-webkit-tap-highlight-color:transparent}button{cursor:pointer}a{color:inherit}::selection{background:#bce7dd;color:#112336}.sr-only{position:absolute;width:1px;height:1px;padding:0;margin:-1px;overflow:hidden;clip:rect(0,0,0,0);white-space:nowrap;border:0}.app-header{position:sticky;top:0;z-index:20;border-bottom:1px solid #d7dde3;background:#fffffff0;-webkit-backdrop-filter:blur(12px);backdrop-filter:blur(12px)}.header-inner{width:min(1440px,calc(100% - 48px));height:68px;margin:0 auto;display:flex;align-items:center;justify-content:space-between;gap:24px}.brand{display:flex;align-items:center;gap:11px;text-decoration:none}.brand-mark{width:38px;height:38px;display:grid;place-items:center;border-radius:7px;background:var(--navy);color:#fff;font-size:13px;font-weight:800;border-bottom:3px solid #22a897}.brand>span:last-child{display:grid;gap:2px}.brand strong{font-size:15px}.brand small{color:var(--muted);font-size:11px}.header-progress{display:flex;align-items:center;gap:18px;color:var(--muted);font-size:13px}.header-progress>span{color:var(--ink);font-weight:700}.text-button{border:0;background:transparent;color:var(--muted);padding:8px}.text-button:hover{color:var(--red)}.library-page,.study-page{width:min(1440px,calc(100% - 48px));margin:0 auto}.library-page{padding:52px 0 80px}.library-intro{display:flex;align-items:flex-end;justify-content:space-between;gap:36px;margin-bottom:30px}.eyebrow{display:block;color:var(--teal);font-size:11px;font-weight:800;letter-spacing:0;text-transform:uppercase}.library-intro h1{margin:8px 0 7px;font-size:36px;line-height:1.2;letter-spacing:0;color:var(--navy)}.library-intro p{margin:0;color:var(--muted);font-size:15px}.snapshot-note{display:grid;grid-template-columns:auto auto;gap:3px 12px;padding-left:22px;border-left:2px solid var(--line)}.snapshot-note span{align-self:end;color:var(--muted);font-size:11px}.snapshot-note strong{grid-row:1 / 3;grid-column:2;font-size:25px;color:var(--navy)}.snapshot-note small{color:var(--muted)}.progress-section{display:grid;grid-template-columns:120px minmax(180px,1fr) auto;align-items:center;gap:26px;padding:19px 22px;border:1px solid var(--line);border-radius:7px;background:var(--surface)}.progress-copy{display:flex;align-items:baseline;gap:12px}.progress-copy strong{color:var(--navy);font-size:23px}.progress-track{height:8px;overflow:hidden;border-radius:4px;background:#e6eaee}.progress-track span{display:block;height:100%;border-radius:4px;background:var(--teal);transition:width .24s ease}.progress-stats{display:flex;align-items:center;gap:18px;color:var(--muted);font-size:12px;white-space:nowrap}.progress-stats>span{display:flex;align-items:center;gap:6px}.status-dot{width:7px;height:7px;border-radius:50%;background:#9ba5b1}.status-dot.mastered{background:var(--green)}.status-dot.reviewing{background:var(--amber)}.filters{margin-top:22px;padding:16px;border:1px solid var(--line);border-radius:7px;background:var(--surface)}.search-wrap{position:relative;display:flex;align-items:center}.search-wrap input{width:100%;height:46px;padding:0 46px 0 42px;border:1px solid #cfd6dd;border-radius:6px;color:var(--ink);outline:none;background:#fbfcfd}.search-wrap input:focus{border-color:var(--teal);box-shadow:0 0 0 3px #d7f0eb;background:#fff}.search-wrap kbd{position:absolute;right:14px;padding:2px 7px;border:1px solid #cbd2d9;border-bottom-width:2px;border-radius:4px;color:var(--muted);background:#fff}.search-icon{position:absolute;left:16px;z-index:1;width:14px;height:14px;border:2px solid #7e8997;border-radius:50%}.search-icon:after{content:"";position:absolute;width:6px;height:2px;right:-5px;bottom:-2px;transform:rotate(45deg);background:#7e8997}.filter-row{display:flex;align-items:flex-end;gap:12px;margin-top:13px}.segmented{display:flex;padding:3px;border:1px solid var(--line);border-radius:6px;background:var(--surface-soft)}.segmented button{min-width:56px;height:33px;border:0;border-radius:4px;background:transparent;color:var(--muted);font-size:12px}.segmented button.active{color:#fff;background:var(--navy)}.select-control{display:grid;gap:4px;color:var(--muted);font-size:10px;font-weight:700}.select-control select{min-width:112px;height:35px;padding:0 30px 0 10px;border:1px solid var(--line);border-radius:5px;color:var(--ink);background:#fff}.filter-toggle{height:35px;padding:0 14px;border:1px solid var(--line);border-radius:5px;color:var(--muted);background:#fff;font-size:12px}.filter-toggle.active{border-color:#e6a9af;color:var(--red);background:var(--red-soft)}.sort-control{margin-left:auto}.results-meta{margin:22px 0 10px;color:var(--muted);font-size:12px}.results-meta strong{color:var(--ink);font-size:15px}.problem-list{overflow:hidden;border:1px solid var(--line);border-radius:7px;background:var(--surface)}.problem-list-head,.problem-row{display:grid;grid-template-columns:64px minmax(250px,2fr) 76px minmax(150px,1fr) 110px 124px 50px;align-items:center;gap:12px}.problem-list-head{min-height:42px;padding:0 16px;border-bottom:1px solid var(--line);color:#7d8793;background:var(--surface-soft);font-size:10px;font-weight:800;text-transform:uppercase}.problem-row{min-height:78px;padding:12px 16px;border-bottom:1px solid #e8ecef;transition:background .15s ease}.problem-row:last-child{border-bottom:0}.problem-row:hover{background:#f8fbfa}.rank{color:#8893a0;font-family:ui-monospace,monospace;font-size:12px;font-weight:700}.problem-name{min-width:0;display:grid;gap:5px}.problem-name a{overflow:hidden;color:var(--navy);font-size:14px;font-weight:750;text-decoration:none;text-overflow:ellipsis;white-space:nowrap}.problem-name a:hover{color:var(--teal)}.problem-name small{overflow:hidden;color:var(--muted);font-size:11px;text-overflow:ellipsis;white-space:nowrap}.difficulty{width:fit-content;min-width:46px;padding:5px 8px;border-radius:4px;font-size:11px;font-weight:700;text-align:center}.difficulty.easy{color:var(--green);background:var(--green-soft)}.difficulty.medium{color:var(--amber);background:var(--amber-soft)}.difficulty.hard{color:var(--red);background:var(--red-soft)}.tag-list{display:flex;flex-wrap:wrap;gap:5px}.tag-list span{padding:4px 7px;border:1px solid #dce2e8;border-radius:4px;color:#556476;background:#f9fafb;font-size:10px}.frequency{display:flex;align-items:center;gap:8px}.frequency strong{width:30px;color:var(--navy);font-size:12px;text-align:right}.frequency-bar{width:50px;height:4px;overflow:hidden;border-radius:2px;background:#e4e8ec}.frequency-bar i{display:block;height:100%;background:#4da89a}.status-select select{width:112px;height:34px;padding:0 8px;border:1px solid var(--line);border-radius:5px;background:#fff;font-size:11px}.status-mastered select{border-color:#a8d5c2;color:var(--green);background:var(--green-soft)}.status-reviewing select{border-color:#e8c785;color:var(--amber);background:var(--amber-soft)}.favorite-button{width:34px;height:34px;border:1px solid transparent;border-radius:5px;color:#8792a0;background:transparent;font-size:21px}.favorite-button:hover,.favorite-button.active{color:#b87405;background:var(--amber-soft)}.empty-state{padding:72px 20px;border:1px solid var(--line);border-radius:7px;text-align:center;background:#fff}.empty-icon{display:grid;place-items:center;width:44px;height:44px;margin:0 auto 14px;border:2px solid #a9b2bc;border-radius:50%;color:#7b8795}.empty-state h2{margin:0;font-size:18px}.empty-state p{color:var(--muted)}.empty-state button,.not-found a{display:inline-flex;align-items:center;justify-content:center;min-height:38px;padding:0 16px;border:0;border-radius:5px;color:#fff;background:var(--teal);text-decoration:none}.study-page{padding:26px 0 80px}.breadcrumb{display:flex;gap:9px;margin-bottom:22px;color:var(--muted);font-size:12px}.breadcrumb a{color:var(--teal);text-decoration:none}.problem-hero{display:grid;grid-template-columns:76px minmax(0,1fr) auto;align-items:start;gap:22px;padding:28px;border:1px solid var(--line);border-radius:7px;background:#fff}.rank-flag{display:grid;place-items:center;width:68px;aspect-ratio:1;border:1px solid #a9d7ce;border-radius:6px;color:var(--teal);background:var(--teal-soft);font-family:ui-monospace,monospace;font-size:12px;font-weight:800}.problem-meta-row{display:flex;align-items:center;gap:12px;color:var(--muted);font-size:11px}.problem-title-block h1{margin:10px 0 8px;color:var(--navy);font-size:30px;line-height:1.25;letter-spacing:0}.problem-title-block>p{margin:0 0 14px;color:var(--muted);line-height:1.7}.problem-actions{display:flex;gap:8px}.problem-actions button,.problem-actions a{min-height:37px;display:inline-flex;align-items:center;gap:6px;padding:0 12px;border:1px solid var(--line);border-radius:5px;color:var(--muted);background:#fff;font-size:12px;text-decoration:none}.problem-actions button.active{color:var(--amber);border-color:#e9c88d;background:var(--amber-soft)}.problem-actions a{color:#fff;border-color:var(--teal);background:var(--teal)}.study-layout{display:grid;grid-template-columns:220px minmax(0,1fr);gap:24px;margin-top:24px}.study-sidebar{align-self:start;position:sticky;top:92px;display:grid;gap:14px}.status-panel,.toc{padding:16px;border:1px solid var(--line);border-radius:7px;background:#fff}.status-actions{display:grid;gap:7px;margin-top:12px}.status-actions button{min-height:34px;border:1px solid var(--line);border-radius:4px;color:var(--muted);background:#fff;font-size:11px;text-align:left;padding:0 10px}.status-actions button.active{border-color:#96cabc;color:var(--teal-dark);background:var(--teal-soft);font-weight:700}.toc{display:grid;gap:5px}.toc>span{margin-bottom:6px;color:var(--ink);font-size:11px;font-weight:800}.toc a{padding:7px 8px;border-left:2px solid transparent;color:var(--muted);font-size:11px;text-decoration:none}.toc a:hover{border-color:var(--teal);color:var(--teal);background:var(--teal-soft)}.solution-content{min-width:0;display:grid;gap:16px}.solution-content>section{display:grid;grid-template-columns:42px minmax(0,1fr);gap:12px;padding:28px;border:1px solid var(--line);border-radius:7px;background:#fff;scroll-margin-top:90px}.section-index{color:#91a0ad;font-family:ui-monospace,monospace;font-size:11px;font-weight:700}.solution-content h2{margin:-4px 0 16px;color:var(--navy);font-size:19px;letter-spacing:0}.solution-content p{color:#4f5e70;font-size:14px;line-height:1.85}.takeaway-section{border-left:3px solid var(--teal)!important;background:#fbfefd!important}.approach-list{list-style:none;display:grid;gap:10px;margin:0;padding:0}.approach-list li{display:grid;grid-template-columns:28px 1fr;gap:10px;align-items:start}.approach-list li>span{display:grid;place-items:center;width:26px;height:26px;border-radius:50%;color:#fff;background:var(--navy);font-size:10px}.approach-list p{margin:0}.code-block{min-width:0;overflow:hidden;border:1px solid #263c52;border-radius:6px;background:#132235}.code-header{height:42px;padding:0 15px;display:flex;align-items:center;justify-content:space-between;border-bottom:1px solid #2a3c51;color:#b7c3d0;font-size:11px}.code-header span{display:flex;align-items:center;gap:8px}.code-header i{width:7px;height:7px;border-radius:50%;background:#46c19f}.code-header button{border:0;color:#cbd5df;background:transparent;font-size:11px}.code-block pre{max-width:100%;margin:0;padding:20px;overflow:auto}.code-block code{color:#e7edf5;font:12px/1.75 SFMono-Regular,Consolas,monospace;white-space:pre}.complexity-grid{display:grid;grid-template-columns:1fr 1fr;gap:12px}.complexity-grid>div{padding:16px;border:1px solid var(--line);border-radius:6px;background:var(--surface-soft)}.complexity-grid span{color:var(--teal);font:10px ui-monospace,monospace}.complexity-grid strong{display:block;margin-top:6px;font-size:12px}.complexity-grid p{margin:6px 0 0}.pitfall-list,.follow-up-list{display:grid;gap:10px;margin:0;padding-left:18px}.pitfall-list li,.follow-up-list li{padding-left:4px;color:#4f5e70;font-size:14px;line-height:1.7}.pitfall-list li::marker{color:var(--red)}.follow-up-list li::marker{color:var(--teal)}.problem-navigator{display:grid;grid-template-columns:1fr 1fr;gap:12px;margin-top:4px}.problem-navigator a{display:grid;gap:6px;min-width:0;padding:15px 18px;border:1px solid var(--line);border-radius:6px;background:#fff;text-decoration:none}.problem-navigator a:hover{border-color:#87bfb3;background:var(--teal-soft)}.problem-navigator a.next{text-align:right}.problem-navigator span{color:var(--muted);font-size:10px}.problem-navigator strong{overflow:hidden;color:var(--navy);font-size:12px;text-overflow:ellipsis;white-space:nowrap}.not-found{min-height:100vh;display:grid;place-content:center;justify-items:center;padding:24px;text-align:center}.not-found>span{color:#a9b3bd;font:800 54px ui-monospace,monospace}.not-found h1{margin:10px 0 0;color:var(--navy)}.not-found p{margin-bottom:24px;color:var(--muted)}:focus-visible{outline:3px solid #72c6b5;outline-offset:2px}@media (max-width: 1100px){.progress-section{grid-template-columns:110px 1fr}.progress-stats{grid-column:1 / -1;justify-content:flex-end}.problem-list-head,.problem-row{grid-template-columns:52px minmax(220px,2fr) 68px minmax(120px,1fr) 105px 42px}.problem-list-head>:nth-child(5),.problem-row>:nth-child(5){display:none}.filter-row{flex-wrap:wrap}.sort-control{margin-left:0}}@media (max-width: 820px){.header-inner,.library-page,.study-page{width:min(100% - 28px,720px)}.library-page{padding-top:34px}.library-intro{align-items:start}.library-intro h1{font-size:29px}.snapshot-note{display:none}.progress-section{grid-template-columns:92px 1fr;gap:14px}.progress-stats{justify-content:flex-start;flex-wrap:wrap}.problem-list-head{display:none}.problem-list{background:transparent;border:0;overflow:visible}.problem-row{grid-template-columns:44px minmax(0,1fr) 38px;grid-template-areas:"rank name favorite" "rank tags status";gap:8px 10px;min-height:100px;margin-bottom:9px;border:1px solid var(--line);border-radius:6px;background:#fff}.problem-row .rank{grid-area:rank;align-self:start;padding-top:4px}.problem-name{grid-area:name}.problem-row .difficulty{display:none}.problem-row .tag-list{grid-area:tags}.problem-row .status-select{grid-area:status;justify-self:end}.problem-row .favorite-button{grid-area:favorite}.status-select select{width:98px}.problem-hero{grid-template-columns:58px 1fr;padding:20px}.rank-flag{width:54px}.problem-title-block h1{font-size:25px}.problem-actions{grid-column:1 / -1;justify-content:flex-end}.study-layout{grid-template-columns:1fr}.study-sidebar{position:static;grid-template-columns:1fr}.toc{display:none}.status-actions{grid-template-columns:repeat(3,1fr)}.status-actions button{text-align:center}}@media (max-width: 520px){.header-inner,.library-page,.study-page{width:calc(100% - 20px)}.header-inner{height:60px}.brand small{display:none}.brand-mark{width:34px;height:34px}.brand strong{font-size:13px}.header-progress>span{display:none}.header-progress{gap:0}.library-intro{margin-bottom:22px}.library-intro h1{font-size:26px}.library-intro p{font-size:13px;line-height:1.6}.progress-section{grid-template-columns:74px minmax(0,1fr);padding:15px}.progress-copy{display:grid;gap:2px}.progress-copy strong{font-size:20px}.progress-stats{gap:10px 14px}.filters{padding:11px}.segmented{width:100%}.segmented button{flex:1;min-width:0}.select-control{flex:1 1 43%}.select-control select{width:100%;min-width:0}.filter-toggle{flex:1 1 100%}.problem-row{grid-template-columns:36px minmax(0,1fr) 34px;padding:11px 10px}.problem-name a{font-size:13px;white-space:normal;line-height:1.45}.problem-name small{display:none}.problem-row .tag-list span:nth-child(2){display:none}.problem-hero{grid-template-columns:1fr;gap:14px;padding:18px}.rank-flag{width:auto;height:31px;aspect-ratio:auto;justify-self:start;padding:0 10px}.problem-meta-row{flex-wrap:wrap}.problem-title-block h1{overflow-wrap:anywhere;font-size:22px}.problem-actions{grid-column:auto;justify-content:flex-start;flex-wrap:wrap}.status-panel{padding:13px}.status-actions{grid-template-columns:1fr}.solution-content>section{grid-template-columns:1fr;padding:20px 16px}.section-index{display:none}.solution-content h2{font-size:17px}.complexity-grid,.problem-navigator{grid-template-columns:1fr}.problem-navigator a.next{text-align:left}.code-block pre{padding:15px}.code-block code{font-size:11px}}