@layer base{*,:before,:after{box-sizing:border-box}[hidden]{display:none!important}html{scroll-behavior:smooth;scroll-padding-top:var(--space-24)}body{background:var(--color-bg);color:var(--color-text);font:1rem/1.65 var(--font-ui);overflow-wrap:break-word;margin:0}a{color:var(--color-link);text-underline-offset:3px}button,input,select,textarea{font:inherit;color:inherit}button,.button{justify-content:center;align-items:center;gap:var(--space-8);min-height:var(--button-height);padding:var(--space-12) var(--space-20);border:1px solid var(--color-border-control);border-radius:var(--radius-control);background:var(--color-surface);color:var(--color-text);box-shadow:var(--shadow-sm);cursor:pointer;transition:background-color var(--duration-fast) var(--ease-standard), transform var(--duration-fast) var(--ease-standard);font-size:.9375rem;font-weight:600;line-height:1.25;text-decoration:none;display:inline-flex}button.primary,.button.primary{background:var(--color-action);color:var(--color-on-action);border-color:var(--color-action)}button:not(:disabled):active,.button:active{background:var(--color-surface-hover)}button.primary:not(:disabled):active,.button.primary:active{background:var(--color-action-active)}button:disabled{color:var(--color-disabled-text);background:var(--color-disabled-bg);border-color:var(--color-disabled-text);box-shadow:none;cursor:not-allowed}input,select,textarea{min-width:0;max-width:100%;min-height:48px;padding:var(--space-12) var(--space-16);border:1px solid var(--color-border-control);border-radius:var(--radius-input);background:var(--color-surface)}input::placeholder{color:var(--color-text-muted);opacity:1}input[aria-invalid=true]{border-color:var(--color-danger)}select:disabled{color:var(--color-disabled-text);background:var(--color-disabled-bg)}:focus-visible{outline:3px solid var(--color-focus);outline-offset:3px}::selection{background:var(--color-selection-bg);color:var(--color-selection-text)}h1,h2,h3,p{margin-top:0}h1,h2,h3{color:var(--color-text);letter-spacing:normal}h1{font-size:var(--page-title-size);line-height:1.3}h2{font-size:var(--section-title-size);line-height:1.25}h3{line-height:1.4}svg{flex-shrink:0}img,video{max-width:100%;height:auto}@media (hover:hover){button:not(:disabled):hover,.button:hover{background:var(--color-surface-hover)}button.primary:not(:disabled):hover,.button.primary:hover{background:var(--color-action-hover)}}@media (prefers-reduced-motion:reduce){html{scroll-behavior:auto}*,:before,:after{transition:none!important;animation:none!important}button.primary:not(:disabled):active,.button.primary:active{transform:none}}}@layer site{.skip-link{top:-100px;left:var(--page-gutter);padding:var(--space-12);z-index:var(--z-sticky);background:var(--color-surface);position:absolute}.skip-link:focus{top:var(--space-8)}.site-header{border-bottom:1px solid var(--color-border-subtle)}.header-inner,.site-main,.site-footer{width:min(var(--content-max), calc(100% - 2 * var(--page-gutter)));margin-inline:auto}.header-inner{min-height:var(--header-height);justify-content:space-between;align-items:center;gap:var(--space-16);display:flex}.brand{align-items:center;gap:var(--space-12);color:var(--color-text);font-size:1.125rem;font-weight:700;line-height:1.4;text-decoration:none;display:flex}.brand-mark{border-radius:var(--radius-control);width:44px;height:44px;color:var(--color-on-action);background:var(--color-brand);place-items:center;display:grid}.brand small{color:var(--color-text-secondary);font-size:.75rem;font-weight:500;display:block}.theme-toggle{min-height:var(--target-min);padding:var(--space-8) var(--space-12);box-shadow:none;font-size:.875rem}.theme-controls{align-items:center;gap:var(--space-4);display:flex}.theme-toggle{border-color:#0000}.site-main{min-height:calc(100vh - var(--header-height) - 100px);padding-bottom:var(--section-gap)}.site-footer{align-items:center;gap:var(--space-4);padding-block:var(--space-24);border-top:1px solid var(--color-border-subtle);color:var(--color-text-secondary);text-align:center;flex-direction:column;font-size:.875rem;display:flex}.footer-dot{margin-inline:var(--space-12)}.intro{align-items:center;gap:var(--space-48);padding-block:var(--section-gap);grid-template-columns:1.2fr 1fr;display:grid}.intro>*{min-width:0}.eyebrow{color:var(--color-text-secondary);margin-bottom:var(--space-16);font-size:.875rem;font-weight:600}.intro h1{max-width:11em;font-size:var(--hero-size);margin-bottom:var(--space-24);line-height:1.25}.intro-description{max-width:32em;color:var(--color-text-secondary);margin-bottom:var(--space-24)}.hero-visual{padding:var(--space-24);border-radius:var(--radius-hero);background:var(--color-surface-subtle);margin:0}.hero-visual svg{width:100%;height:auto;display:block}.hero-visual figcaption{text-align:center;color:var(--color-text-secondary);margin-top:var(--space-12);font-size:.875rem}.reading-path{gap:var(--space-24);padding:var(--space-24) 0;margin:0 0 var(--section-gap);border-block:1px solid var(--color-border-subtle);grid-template-columns:repeat(3,1fr);list-style:none;display:grid}.reading-path li{align-items:start;gap:var(--space-12);display:flex}.reading-path b{border-radius:var(--radius-control);width:44px;height:44px;color:var(--color-selection-text);background:var(--color-selection-bg);font-variant-numeric:tabular-nums;flex-shrink:0;place-items:center;display:grid}.reading-path strong{margin-bottom:var(--space-4);display:block}.reading-path p{color:var(--color-text-secondary);margin:0;font-size:.875rem}.section-title{align-items:baseline;gap:var(--space-16);margin-bottom:var(--space-24);flex-wrap:wrap;display:flex}.section-title h2{margin:0}.section-title>span,.result-count{color:var(--color-text-secondary);font-size:.875rem}.filters{align-items:end;gap:var(--space-16);padding:var(--space-24);background:var(--color-surface-subtle);border-radius:var(--radius-card);display:flex}.filters label{gap:var(--space-8);flex-direction:column;min-width:0;display:flex}.filters label>span{font-size:.875rem;font-weight:600}.search-field{flex:1}.filters select{min-width:136px}.clear-button{min-height:48px;box-shadow:none}.result-count{margin-block:var(--space-20)}.problem-list{gap:var(--grid-gap);grid-template-columns:repeat(3,minmax(0,1fr));display:grid}.problem-card{min-width:0;padding:var(--space-24);border:2px solid var(--color-border-subtle);border-radius:var(--radius-card);background:var(--color-surface);flex-direction:column;align-items:start;display:flex}.problem-number{align-items:baseline;gap:var(--space-8);color:var(--color-text-secondary);margin-bottom:var(--space-20);font-size:.875rem;display:flex}.problem-number b{color:var(--color-text);font-variant-numeric:tabular-nums;font-size:1.125rem}.problem-card-body{flex:1;width:100%;min-width:0}.card-title{align-items:center;gap:var(--space-12);margin-bottom:var(--space-8);flex-wrap:wrap;display:flex}.card-title h3{overflow-wrap:anywhere;min-width:0;margin:0;font-size:1.125rem;font-weight:600}.card-title a{min-height:var(--target-min);color:var(--color-text);align-items:center;text-decoration-thickness:1px;display:inline-flex}.difficulty,.tags span{min-height:28px;padding:var(--space-4) 10px;border-radius:var(--radius-pill);align-items:center;font-size:.8125rem;font-weight:600;line-height:1.25;display:inline-flex}.difficulty.easy{color:var(--color-success);background:var(--color-success-bg)}.difficulty.medium{color:var(--color-warning);background:var(--color-warning-bg)}.difficulty.hard{color:var(--color-danger);background:var(--color-danger-bg)}.card-meta{align-items:start;gap:var(--space-16);color:var(--color-text-muted);flex-direction:column;font-size:.875rem;display:flex}.problem-card p{color:var(--color-text-secondary);margin-bottom:var(--space-20)}.tags{gap:var(--space-8);flex-wrap:wrap;display:flex}.tags span{background:var(--color-surface-subtle);color:var(--color-text-secondary)}.card-arrow{width:100%;margin-top:var(--space-24);justify-content:space-between}.empty-state{padding:var(--space-40) var(--space-20);text-align:center;background:var(--color-surface-subtle);border-radius:var(--radius-card)}.empty-state h3{font-size:1.125rem}.empty-state p{color:var(--color-text-secondary)}.not-found{padding-block:var(--section-gap);max-width:var(--reading-max)}.not-found>p{color:var(--color-text-secondary)}@media (hover:hover){.brand:hover,.card-title a:hover{color:var(--color-link)}}@media (width<=1023px){.intro{gap:var(--space-24)}.problem-list{grid-template-columns:repeat(2,minmax(0,1fr))}.filters{flex-wrap:wrap}.filters .search-field{flex-basis:100%}.filters label:not(.search-field){flex:1}.filters select{width:100%;min-width:0}}@media (width<=767px){.theme-toggle>span{display:none}.brand{gap:var(--space-8);font-size:1rem}.brand small{display:none}.intro{grid-template-columns:1fr}.intro h1{max-width:none}.hero-visual{justify-self:center;width:100%;max-width:440px}.reading-path{grid-template-columns:1fr}}@media (width<=639px){.problem-list{gap:var(--space-16);grid-template-columns:minmax(0,1fr)}.problem-card,.filters{padding:var(--space-20)}.clear-button,.intro .button{width:100%}}@media (width<=359px){.header-inner{padding-block:var(--space-8);flex-wrap:wrap}.filters label:not(.search-field){flex-basis:100%}}}@layer article,demo;:root{color-scheme:light;--color-bg:#f8fafc;--color-surface:#fff;--color-surface-subtle:#f1f5f9;--color-surface-hover:#e2e8f0;--color-text:#0f172a;--color-text-secondary:#475569;--color-text-muted:#5b6b80;--color-border-subtle:#e2e8f0;--color-border-control:#64748b;--color-brand:#2563eb;--color-action:#2563eb;--color-action-hover:#1d4ed8;--color-action-active:#1e40af;--color-on-action:#fff;--color-link:#1d4ed8;--color-focus:#2563eb;--color-selection-bg:#eff6ff;--color-selection-text:#1d4ed8;--color-disabled-bg:#e2e8f0;--color-disabled-text:#475569;--color-success:#166534;--color-success-bg:#f0fdf4;--color-warning:#9a3412;--color-warning-bg:#fff7ed;--color-danger:#b42336;--color-danger-bg:#fdecef;--color-info:#1d4ed8;--color-info-bg:#eff6ff;--color-hash:#6b21a8;--color-hash-bg:#faf5ff;--color-danger-action:#b42336;--color-on-danger:#fff;--font-ui:-apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", "Noto Sans CJK SC", sans-serif;--font-mono:ui-monospace, SFMono-Regular, Consolas, "Liberation Mono", monospace;--space-4:.25rem;--space-8:.5rem;--space-12:.75rem;--space-16:1rem;--space-20:1.25rem;--space-24:1.5rem;--space-32:2rem;--space-40:2.5rem;--space-48:3rem;--space-64:4rem;--space-80:5rem;--space-96:6rem;--space-120:7.5rem;--radius-control:8px;--radius-card:12px;--radius-hero:16px;--radius-dialog:16px;--radius-input:8px;--radius-menu:8px;--radius-pill:9999px;--content-max:1280px;--reading-max:720px;--practice-max:100%;--page-gutter:16px;--header-height:64px;--section-gap:48px;--grid-gap:24px;--button-height:44px;--target-min:44px;--hero-size:clamp(2rem, 4vw, 2.5rem);--section-title-size:clamp(1.5rem, 2vw, 1.625rem);--page-title-size:clamp(1.75rem, 3vw, 2.25rem);--duration-fast:.12s;--duration-normal:.18s;--duration-slow:.24s;--ease-standard:cubic-bezier(.2, .8, .2, 1);--shadow-sm:none;--shadow-popover:0 12px 32px #0f172a24;--z-sticky:20;--z-dropdown:40;--z-overlay:60;--z-dialog:70;--z-toast:80;--z-tooltip:90}@media (width>=768px){:root{--page-gutter:24px}}@media (width>=1024px){:root{--page-gutter:32px;--header-height:72px}}:root[data-theme=dark]{color-scheme:dark;--color-bg:#0b1220;--color-surface:#111c2e;--color-surface-subtle:#19263b;--color-surface-hover:#25364e;--color-text:#f1f5f9;--color-text-secondary:#cbd5e1;--color-text-muted:#94a3b8;--color-border-subtle:#334155;--color-border-control:#94a3b8;--color-brand:#60a5fa;--color-action:#60a5fa;--color-action-hover:#93c5fd;--color-action-active:#bfdbfe;--color-on-action:#0b1220;--color-link:#93c5fd;--color-focus:#93c5fd;--color-selection-bg:#172e50;--color-selection-text:#bfdbfe;--color-disabled-bg:#25364e;--color-disabled-text:#cbd5e1;--color-success:#86efac;--color-success-bg:#143326;--color-warning:#fdba74;--color-warning-bg:#3f251a;--color-danger:#fda4af;--color-danger-bg:#40232f;--color-info:#bfdbfe;--color-info-bg:#172e50;--color-hash:#d8b4fe;--color-hash-bg:#302046;--shadow-popover:0 12px 32px #0006}