.book-index[data-astro-cid-4ojkswfr]{width:min(1200px,92%);margin-inline:auto;padding:2rem 0 5rem}.index-header[data-astro-cid-4ojkswfr]{margin:0 0 1.7rem}.index-header[data-astro-cid-4ojkswfr] h1[data-astro-cid-4ojkswfr]{margin:0 0 .35rem;font-size:clamp(1.9rem,3.5vw,2.5rem);line-height:1.35}.index-header[data-astro-cid-4ojkswfr] p[data-astro-cid-4ojkswfr]{color:var(--muted);margin:0}.subject-button[data-astro-cid-4ojkswfr],.subject-panel[data-astro-cid-4ojkswfr],[data-astro-cid-4ojkswfr][data-subject=classical-mechanics]{--subject-color:#0f766e;--subject-soft:#f0fdfa}[data-astro-cid-4ojkswfr][data-subject=mathematics],[data-astro-cid-4ojkswfr][data-subject=mathematical-physics]{--subject-color:#4338ca;--subject-soft:#eef2ff}[data-astro-cid-4ojkswfr][data-subject=electrodynamics]{--subject-color:#1d4ed8;--subject-soft:#eff6ff}[data-astro-cid-4ojkswfr][data-subject=thermodynamics]{--subject-color:#b45309;--subject-soft:#fffbeb}[data-astro-cid-4ojkswfr][data-subject=quantum-mechanics]{--subject-color:#6d28d9;--subject-soft:#f5f3ff}[data-astro-cid-4ojkswfr][data-subject=relativity]{--subject-color:#be185d;--subject-soft:#fdf2f8}.subject-picker[data-astro-cid-4ojkswfr]{flex-wrap:wrap;gap:.65rem;margin:0 0 2rem;display:flex}.subject-button[data-astro-cid-4ojkswfr]{border:1.5px solid var(--subject-color);background:var(--subject-soft);color:var(--subject-color);opacity:.68;cursor:pointer;box-shadow:none;border-radius:9px;outline:none;justify-content:center;align-items:center;gap:.5rem;padding:.4rem .85rem;font-weight:700;line-height:1.5;transition:opacity .18s,background .18s,transform .18s;display:inline-flex}.subject-button-text[data-astro-cid-4ojkswfr]{white-space:nowrap}.subject-introduction[data-astro-cid-4ojkswfr]{margin:0 0 2rem;padding:0}.subject-introduction[data-astro-cid-4ojkswfr] h2[data-astro-cid-4ojkswfr]{color:var(--subject-color);margin:0 0 .5rem;font-family:Li Subha Letterpress Unicode,AdorshoLipi,sans-serif;font-size:1.6rem;font-weight:700;line-height:1.5}.subject-introduction[data-astro-cid-4ojkswfr] p[data-astro-cid-4ojkswfr]{color:var(--foreground);margin:0;font-family:AdorshoLipi,sans-serif;font-size:1.05rem;line-height:1.85}.subject-icon-box[data-astro-cid-4ojkswfr]{background:#ffffff73;border-radius:7px;flex:0 0 34px;justify-content:center;align-items:center;width:34px;height:34px;display:inline-flex}.subject-icon-box[data-astro-cid-4ojkswfr] img{object-fit:contain;width:30px;height:30px;display:block}.subject-button[data-astro-cid-4ojkswfr]:not(.active) .subject-icon-box[data-astro-cid-4ojkswfr]{opacity:.8}.subject-button[data-astro-cid-4ojkswfr].active{opacity:1;background:var(--subject-color);color:#fff;border-color:var(--subject-color);box-shadow:none;outline:none}.subject-button[data-astro-cid-4ojkswfr].active .subject-icon-box[data-astro-cid-4ojkswfr]{opacity:1;background:#fffffff5}.subject-button[data-astro-cid-4ojkswfr]:focus-visible,.lesson-card[data-astro-cid-4ojkswfr]:focus-visible{outline:2px solid var(--subject-color);outline-offset:3px}.subject-panel[data-astro-cid-4ojkswfr][hidden]{display:none!important}.chapter-section[data-astro-cid-4ojkswfr]{margin:0 0 2.7rem}.chapter-heading[data-astro-cid-4ojkswfr]{border-bottom:2px dotted var(--subject-color);color:var(--foreground);margin:0 0 1.25rem;padding-bottom:.2rem;font-family:Li Subha Letterpress Unicode,AdorshoLipi,sans-serif;font-size:clamp(1.5rem,2.25vw,2rem);font-weight:700;line-height:1.5}.lesson-grid[data-astro-cid-4ojkswfr]{grid-template-columns:repeat(3,minmax(0,1fr));gap:12px;padding:0;display:grid}.lesson-card[data-astro-cid-4ojkswfr]{border:1.5px solid var(--subject-color);min-width:0;min-height:124px;color:var(--subject-color);text-align:center;overflow-wrap:anywhere;background:#fafafa;border-radius:11px;justify-content:center;align-items:flex-start;padding:14px 16px;font-family:Li Subha Letterpress Unicode,AdorshoLipi,sans-serif;font-size:clamp(1.12rem,1.8vw,1.5rem);line-height:1.5;text-decoration:none;transition:background .18s,transform .18s,box-shadow .18s;display:flex}.chapter-landing-card[data-astro-cid-4ojkswfr]{background:var(--subject-soft);flex-direction:column;justify-content:center;align-items:center;gap:.15rem}.chapter-landing-label[data-astro-cid-4ojkswfr]{letter-spacing:.01em;opacity:.8;font-size:.79rem;font-weight:700}.chapter-landing-title[data-astro-cid-4ojkswfr]{font-weight:700}.chapter-landing-action[data-astro-cid-4ojkswfr]{font-size:.82rem;font-weight:700}a[data-astro-cid-4ojkswfr].lesson-card:hover{background:var(--subject-soft);transform:translateY(-2px);box-shadow:0 4px 12px #0f172a1a}.lesson-card[data-astro-cid-4ojkswfr].unpublished{color:var(--subject-color);background:var(--subject-soft);cursor:default;border-style:dashed}.no-content[data-astro-cid-4ojkswfr]{color:var(--muted);padding:.5rem .75rem}.subject-references[data-astro-cid-4ojkswfr]{border:1px solid var(--subject-color);background:var(--subject-soft);border-radius:12px;margin-top:3rem;padding:1.7rem 1.9rem}.references-eyebrow[data-astro-cid-4ojkswfr]{color:var(--subject-color);margin:0 0 .2rem;font-size:.82rem;font-weight:700}.subject-references[data-astro-cid-4ojkswfr] h2[data-astro-cid-4ojkswfr]{color:var(--foreground);margin:0 0 .7rem;font-family:Li Subha Letterpress Unicode,AdorshoLipi,sans-serif;font-size:clamp(1.25rem,2.3vw,1.6rem)}.references-intro[data-astro-cid-4ojkswfr],.references-empty[data-astro-cid-4ojkswfr]{color:var(--muted);margin:0;line-height:1.8}.references-list[data-astro-cid-4ojkswfr]{margin:1.2rem 0 0;padding:0;list-style:none}.reference-item[data-astro-cid-4ojkswfr]{border-top:1px solid color-mix(in srgb, var(--subject-color) 22%, transparent);gap:.8rem;padding:.9rem 0;display:flex}.reference-number[data-astro-cid-4ojkswfr]{color:var(--subject-color);flex:0 0 1.8rem;font-weight:700}.reference-details[data-astro-cid-4ojkswfr]{flex-direction:column;gap:.1rem;min-width:0;display:flex}.reference-title[data-astro-cid-4ojkswfr]{font-style:normal;font-weight:700}.reference-title[data-astro-cid-4ojkswfr] a[data-astro-cid-4ojkswfr]{color:var(--subject-color);text-decoration:none}.reference-title[data-astro-cid-4ojkswfr] a[data-astro-cid-4ojkswfr]:hover{text-decoration:underline}.reference-authors[data-astro-cid-4ojkswfr]{color:var(--foreground)}.reference-meta[data-astro-cid-4ojkswfr]{color:var(--muted);font-size:.92rem}.reference-title[data-astro-cid-4ojkswfr] a[data-astro-cid-4ojkswfr]:focus-visible{outline:2px solid var(--subject-color);outline-offset:3px}@media (width<=950px){.lesson-grid[data-astro-cid-4ojkswfr]{grid-template-columns:repeat(2,minmax(0,1fr))}}@media (width<=600px){.book-index[data-astro-cid-4ojkswfr]{padding-top:1.5rem}.subject-picker[data-astro-cid-4ojkswfr]{gap:.5rem;margin-bottom:1.75rem}.subject-button[data-astro-cid-4ojkswfr]{padding:.35rem .65rem}.subject-icon-box[data-astro-cid-4ojkswfr]{flex-basis:28px;width:28px;height:28px}.subject-icon-box[data-astro-cid-4ojkswfr] img{width:25px;height:25px}.chapter-heading[data-astro-cid-4ojkswfr]{margin-bottom:1rem}.lesson-grid[data-astro-cid-4ojkswfr]{grid-template-columns:1fr}.lesson-card[data-astro-cid-4ojkswfr]{min-height:90px;padding:12px 14px}.chapter-section[data-astro-cid-4ojkswfr]{margin-bottom:2.4rem}.subject-references[data-astro-cid-4ojkswfr]{padding:1.2rem}}@media (prefers-reduced-motion:reduce){.subject-button[data-astro-cid-4ojkswfr],.lesson-card[data-astro-cid-4ojkswfr]{transition:none}}.subject-button[data-astro-cid-4ojkswfr]{opacity:1}.subject-button[data-astro-cid-4ojkswfr]:not(.active){opacity:1;color:color-mix(in srgb, var(--subject-color) 65%, white);border-color:color-mix(in srgb, var(--subject-color) 65%, white);background:var(--subject-soft)}.subject-button[data-astro-cid-4ojkswfr] .subject-icon-box[data-astro-cid-4ojkswfr],.subject-button[data-astro-cid-4ojkswfr] .subject-icon-box[data-astro-cid-4ojkswfr] img{opacity:1!important;filter:none!important}.subject-button[data-astro-cid-4ojkswfr].active{opacity:1;color:#fff;background:var(--subject-color);border-color:var(--subject-color)}.subject-button[data-astro-cid-4ojkswfr]:hover:not(.active){opacity:1;transform:translateY(-1px)}