.problem-page{--problem-bg: #ffffff;--problem-surface: #ffffff;--problem-surface-2: #f7f7f8;--problem-surface-3: #f0f0f0;--problem-border: #e5e7eb;--problem-border-2: #cfcfdb;--problem-text: #1f1633;--problem-text-2: #514b5c;--problem-muted: #746f7b;--problem-faint: #9b96a3;--problem-blue: #150f23;--problem-on-accent: #ffffff;--problem-blue-soft: #cfcfdb;--problem-blue-tint: #f0f0f0;--problem-violet: #6a5fc1;--problem-on-violet: #ffffff;--problem-violet-tint: #f1eff7;--problem-success: #008817;--problem-success-tint: #ecf3ec;--problem-error: #b50909;--problem-error-tint: #f4e3db;--problem-on-status: #ffffff;--problem-fs-hero-title: 1.75rem;--problem-fs-hero-description: 1.0625rem;--problem-fs-body: .9375rem;--problem-fs-chip: .875rem;--problem-fs-breadcrumb: .84375rem;--problem-lh-hero-title: 1.12;--problem-lh-reading: 1.78;--problem-lh-body: 1.6;--problem-lh-compact: 1.4;--color-math-bg: var(--problem-surface-2)}html.dark .problem-page{--problem-bg: #0c0f14;--problem-surface: #161b23;--problem-surface-2: #1b212b;--problem-surface-3: #232a35;--problem-border: #272e3a;--problem-border-2: #333c49;--problem-text: #e9edf3;--problem-text-2: #bec6d2;--problem-muted: #8c96a5;--problem-faint: #697283;--problem-blue: #b7adff;--problem-on-accent: #150f23;--problem-blue-soft: #d2cbff;--problem-blue-tint: rgba(106, 95, 193, .24);--problem-violet: #b7adff;--problem-on-violet: #150f23;--problem-violet-tint: rgba(106, 95, 193, .22);--problem-success: #70e17b;--problem-success-tint: rgba(112, 225, 123, .14);--problem-error: #f39268;--problem-error-tint: rgba(243, 146, 104, .14);--problem-on-status: #150f23;--color-math-bg: var(--problem-surface-2)}@media(min-width:640px){.problem-page{--problem-fs-hero-title: 2.0625rem;--problem-fs-hero-description: 1.125rem}}.problem-card{border:1px solid var(--problem-border);border-radius:8px;background:var(--problem-surface);padding:18px;box-shadow:0 1px 2px #141e370a,0 4px 14px #141e370d}html.dark .problem-card{box-shadow:0 1px 2px #00000059,0 6px 18px #00000047}.problem-chip,.problem-tag,.problem-badge,.problem-card-chip{display:inline-flex;align-items:center;font-weight:600;line-height:1.2}.problem-breadcrumb{font-size:var(--problem-fs-breadcrumb);line-height:var(--problem-lh-compact)}.problem-chip{border-radius:6px;border:1px solid var(--problem-border);background:var(--problem-surface-2);color:var(--problem-text-2);padding:6px 10px;font-size:12px}.problem-tag{border-radius:7px;background:var(--problem-surface-3);color:var(--problem-muted);padding:4px 12px;font-size:var(--problem-fs-chip);line-height:var(--problem-lh-compact);transition:background-color .15s ease,color .15s ease}.problem-tag:hover{background:var(--problem-surface-2);color:var(--problem-text-2)}.problem-badge{border-radius:7px;background:var(--problem-surface-3);color:var(--problem-muted);padding:4px 12px;font-size:var(--problem-fs-chip);line-height:var(--problem-lh-compact)}.problem-badge-primary{background:var(--problem-blue-tint);color:var(--problem-blue)}.problem-badge-accent{background:var(--problem-violet-tint);color:var(--problem-violet)}.problem-hero-title{font-size:var(--problem-fs-hero-title);line-height:var(--problem-lh-hero-title)}.problem-hero-description{font-size:var(--problem-fs-hero-description);line-height:var(--problem-lh-reading)}.problem-meta{font-size:var(--problem-fs-body);line-height:var(--problem-lh-body)}.problem-card-chip{border-radius:6px;border:1px solid var(--problem-border);background:var(--problem-surface-2);color:var(--problem-muted);padding:4px 7px;font-size:11px}.problem-button{border:1px solid var(--problem-border);border-radius:8px;background:var(--problem-surface-2);color:var(--problem-text-2);min-height:38px;padding:0 10px;font:inherit;font-size:12px;font-weight:600;cursor:pointer;transition:border-color .15s ease,background-color .15s ease,color .15s ease}.problem-button:hover{border-color:var(--problem-blue-soft);color:var(--problem-text)}.problem-record-card{width:min(100%,760px);margin-right:auto;margin-left:auto;border-color:color-mix(in srgb,var(--problem-border) 72%,var(--problem-blue-soft));background:linear-gradient(180deg,color-mix(in srgb,var(--problem-surface) 94%,var(--problem-violet-tint)) 0%,var(--problem-surface) 64%);padding:14px;box-shadow:0 18px 40px #1f163314,0 1px 2px #1f16330d}html.dark .problem-record-card{background:linear-gradient(180deg,color-mix(in srgb,var(--problem-surface) 88%,var(--problem-violet-tint)) 0%,var(--problem-surface) 68%);box-shadow:0 16px 34px #00000057,0 1px 2px #00000073}.problem-record-header{display:flex;align-items:center;justify-content:space-between;gap:12px}.problem-record-title{color:var(--problem-text);font-size:13px;font-weight:800;line-height:1.35}.problem-record-actions{display:grid;grid-template-columns:minmax(0,1fr) auto;gap:8px;align-items:center;margin-top:12px}.problem-record-result-group{display:grid;min-width:0;grid-template-columns:repeat(2,minmax(0,1fr));gap:4px;border:1px solid var(--problem-border);border-radius:8px;background:var(--problem-surface-2);padding:3px}.problem-record-button{display:inline-flex;min-height:32px;align-items:center;justify-content:center;gap:6px;border:0;border-radius:6px;background:transparent;padding:0 10px;color:var(--problem-muted);font-size:12px;font-weight:800}.problem-record-button[data-problem-result=correct] span{color:var(--problem-success)}.problem-record-button[data-problem-result=incorrect] span{color:var(--problem-error)}.problem-record-button[data-problem-result=correct]:hover{background:var(--problem-success-tint);color:var(--problem-success)}.problem-record-button[data-problem-result=incorrect]:hover{background:var(--problem-error-tint);color:var(--problem-error)}.problem-record-button[data-problem-result=correct][data-active=true]{background:var(--problem-success);color:var(--problem-on-status)}.problem-record-button[data-problem-result=incorrect][data-active=true]{background:var(--problem-error);color:var(--problem-on-status)}.problem-record-button[data-active=true]{box-shadow:0 1px 2px #1f16331f}.problem-record-button[data-active=true] span{color:currentColor}.problem-record-clear{width:auto;min-height:34px;border-radius:999px;background:transparent;padding:0 12px;color:var(--problem-faint);white-space:nowrap}.problem-record-clear:hover{background:var(--problem-surface-2)}.problem-record-status{display:inline-flex;min-height:24px;align-items:center;justify-content:center;border-radius:999px;background:var(--problem-surface-2);color:var(--problem-muted);padding:3px 9px;text-align:center;font-size:11px;font-weight:700;line-height:1.35;white-space:nowrap}.problem-record-note-header{display:flex;align-items:baseline;justify-content:space-between;gap:12px;margin-top:12px;color:var(--problem-faint);font-size:11px;font-weight:700;line-height:1.35}.problem-record-note-header label{color:var(--problem-muted)}.problem-record-note{display:block;width:100%;height:82px;margin-top:6px;resize:none;border:1px solid var(--problem-border);border-radius:8px;background:color-mix(in srgb,var(--problem-surface-2) 74%,var(--problem-surface));color:var(--problem-text);padding:10px 11px;font:inherit;font-size:13px;line-height:1.6;outline:none;transition:border-color .15s ease,background-color .15s ease,box-shadow .15s ease}.problem-record-note::placeholder{color:var(--problem-faint)}.problem-record-note:focus{border-color:var(--problem-blue-soft);background:var(--problem-surface);box-shadow:0 0 0 3px color-mix(in srgb,var(--problem-blue-soft) 28%,transparent)}@media(max-width:520px){.problem-record-actions{grid-template-columns:1fr}.problem-record-clear{width:100%}}.problem-step-link{display:flex;width:100%;align-items:center;gap:8px;border:0;border-radius:8px;background:transparent;color:var(--problem-muted);padding:8px;text-align:left;font:inherit;cursor:pointer;transition:background-color .15s ease,color .15s ease}.problem-step-link:hover,.problem-step-link[data-active=true]{background:var(--problem-surface-2);color:var(--problem-text)}.problem-step-detail-frame{--problem-detail-row: 48px;--problem-detail-gap: 4px;--problem-detail-height: 152px;--problem-detail-offset: 0px;position:relative;height:var(--problem-detail-height);overflow:hidden}.problem-step-detail-frame:before,.problem-step-detail-frame:after{position:absolute;right:0;left:0;z-index:2;height:18px;pointer-events:none;content:"";opacity:0;transition:opacity .16s ease}.problem-step-detail-frame:before{top:0;background:linear-gradient(to bottom,var(--problem-surface),transparent)}.problem-step-detail-frame:after{bottom:0;background:linear-gradient(to top,var(--problem-surface),transparent)}.problem-step-detail-frame[data-shadow-top=true]:before,.problem-step-detail-frame[data-shadow-bottom=true]:after{opacity:1}.problem-step-detail-track{display:flex;flex-direction:column;gap:var(--problem-detail-gap);margin:0;padding:0;list-style:none;transform:translateY(var(--problem-detail-offset));transition:transform .22s ease;will-change:transform}.problem-step-detail-frame[data-ready=false] .problem-step-detail-track{transition:none}.problem-step-detail-track>li{height:var(--problem-detail-row);flex:0 0 var(--problem-detail-row);transition:opacity .18s ease,filter .18s ease,transform .18s ease}.problem-step-detail-track .problem-step-link{height:100%;align-items:center;padding-top:6px;padding-bottom:6px;transition:background-color .15s ease,color .15s ease,opacity .18s ease,filter .18s ease,transform .18s ease}.problem-step-detail-track .problem-step-label{display:-webkit-box;overflow:hidden;-webkit-box-orient:vertical;-webkit-line-clamp:2;line-height:1.32}.problem-step-detail-track>li[data-detail-position=past] .problem-step-link{opacity:.56;filter:saturate(.75)}.problem-step-detail-track>li[data-detail-position=future] .problem-step-link{opacity:.72;filter:saturate(.86)}.problem-step-detail-track>li[data-detail-position=current] .problem-step-link{opacity:1;filter:none;transform:translate(1px)}.problem-step-detail-frame[data-center-focus=true]:before{height:46px;background:linear-gradient(to bottom,var(--problem-surface) 0%,color-mix(in srgb,var(--problem-surface) 76%,transparent) 48%,transparent 100%)}.problem-step-detail-frame[data-center-focus=true]:after{height:42px;background:linear-gradient(to top,var(--problem-surface) 0%,color-mix(in srgb,var(--problem-surface) 68%,transparent) 45%,transparent 100%)}@media(prefers-reduced-motion:reduce){.problem-step-detail-track,.problem-step-detail-track>li,.problem-step-detail-track .problem-step-link,.problem-step-detail-frame:before,.problem-step-detail-frame:after{transition:none}}.problem-step-marker{display:inline-flex;width:20px;height:20px;flex:0 0 auto;align-items:center;justify-content:center;border-radius:50%;background:var(--problem-surface-3);color:var(--problem-muted);font-size:11px;font-weight:700}.problem-step-link[data-active=true] .problem-step-marker{background:var(--problem-blue);color:var(--problem-on-accent)}.problem-step-label{min-width:0;flex:1 1 auto;overflow-wrap:anywhere;line-height:1.45}.problem-mini-badge{display:inline-flex;min-width:48px;align-items:center;justify-content:center;border-radius:8px;background:var(--problem-violet-tint);color:var(--problem-blue);padding:7px;text-align:center;font-size:11px;font-weight:700;line-height:1.35}.problem-prose{color:var(--problem-text-2);font-size:1.05rem;line-height:1.78;text-align:center}.problem-prose h2{border-top:1px solid var(--problem-border);color:var(--problem-text);font-family:var(--font-sans);font-size:1.4375rem;line-height:1.28;margin:1.5em 0 1em;padding-top:1.25em}.problem-prose h2:first-child{border-top:0;margin-top:0;padding-top:0}.problem-prose h3{position:relative;width:min(100%,760px);border-top:1px solid color-mix(in srgb,var(--problem-border) 78%,transparent);color:var(--problem-text);font-family:var(--font-sans);font-size:1.3rem;font-weight:800;line-height:1.35;margin:2.35em auto .95em;padding-top:1.05em;scroll-margin-top:84px;text-align:center}.problem-prose h3:before{position:absolute;top:-2px;left:50%;width:44px;height:3px;border-radius:999px;background:var(--problem-violet);content:"";transform:translate(-50%)}.problem-prose h2+h3{margin-top:1.25em}@media(max-width:520px){.problem-prose h3{font-size:1.18rem;line-height:1.42;margin-top:2.15em;padding-top:.9em}}.problem-prose p,.problem-prose li{color:var(--problem-text-2)}.problem-prose p{margin-top:1.5em;margin-bottom:1.5em}.problem-prose p:first-child{margin-top:0}.problem-prose p:last-child{margin-bottom:0}.problem-prose strong{color:var(--problem-text);font-weight:700}.problem-prose a{color:var(--problem-blue);text-decoration-color:var(--problem-blue-soft);text-underline-offset:3px}.problem-prose hr{border-color:var(--problem-border);margin:28px 0}.problem-prose figure{margin:28px 0}.problem-prose img{border:0;border-radius:8px;background:var(--problem-surface)}.problem-prose img[data-problem-lightbox-image]{cursor:zoom-in}.problem-prose img[data-problem-lightbox-image]:focus-visible{outline:3px solid var(--problem-blue-soft);outline-offset:3px}.problem-prose figcaption{color:var(--problem-muted);font-size:12px;line-height:1.6;margin-top:8px;text-align:center}.problem-prose .katex-display{border-color:transparent;background:color-mix(in srgb,var(--problem-surface-2) 40%,transparent)}@media(min-width:1024px){.problem-prose img{width:80%;max-width:100%;margin-right:auto;margin-left:auto;box-sizing:border-box}.problem-prose .katex-display{width:80%;max-width:100%;margin:18px auto!important;box-sizing:border-box}}