:root{--background:#0f1115;--surface:#171a21;--surface-hover:#1d212a;--border:#262b35;--text:#f5f7fa;--text-muted:#98a2b3;--accent:#22c55e;--accent-soft:rgba(34,197,94,0.12);--radius:12px}*{box-sizing:border-box;margin:0;padding:0}body{background-color:var(--background);color:var(--text);font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Helvetica,Arial,sans-serif;line-height:1.6;-webkit-font-smoothing:antialiased}a{color:inherit;text-decoration:none}.page{max-width:1040px;margin:0 auto;padding:48px 24px 96px}.site-header{margin-bottom:32px}.logo{font-size:2.2rem;font-weight:800;letter-spacing:-.02em}.logo-accent{color:var(--accent)}.tagline{color:var(--text-muted);font-size:1.05rem}.search-input{width:100%;padding:14px 18px;font-size:1rem;color:var(--text);background-color:var(--surface);border:1px solid var(--border);border-radius:var(--radius);outline:none;transition:border-color .2s}.search-input:focus{border-color:var(--accent)}.search-input::placeholder{color:var(--text-muted)}.category-filter{display:flex;flex-wrap:wrap;gap:10px;margin:20px 0 36px}.category-button{padding:8px 18px;font-size:.95rem;color:var(--text-muted);background-color:var(--surface);border:1px solid var(--border);border-radius:999px;cursor:pointer;transition:border-color .2s,color .2s}.category-button:hover{border-color:var(--accent);color:var(--text)}.category-button.active{color:#0f1115;background-color:var(--accent);border-color:var(--accent);font-weight:600}.course-grid{display:grid;grid-template-columns:repeat(3,1fr);grid-gap:24px;gap:24px}.course-card{display:block;background-color:var(--surface);border:1px solid var(--border);border-radius:var(--radius);overflow:hidden;transition:transform .2s,border-color .2s}.course-card:hover{transform:translateY(-4px);border-color:var(--accent)}.course-thumbnail{display:block;width:100%;aspect-ratio:3/2;object-fit:cover}.course-card-body{padding:18px}.course-card-title{font-size:1.15rem;margin:10px 0 2px}.lesson-count{color:var(--text-muted);font-size:.9rem;margin-bottom:14px}.category-badge{display:inline-block;padding:3px 12px;font-size:.78rem;font-weight:600;color:var(--accent);background-color:var(--accent-soft);border-radius:999px}.progress-row{display:flex;align-items:center;gap:12px}.progress-track{flex:1 1;height:8px;background-color:var(--border);border-radius:999px;overflow:hidden}.progress-fill{height:100%;background-color:var(--accent);border-radius:999px;transition:width .3s}.progress-text{min-width:42px;text-align:right;font-size:.85rem;font-weight:600;color:var(--text-muted)}.back-link{display:inline-block;color:var(--text-muted);font-size:.95rem;margin-bottom:28px;transition:color .2s}.back-link:hover{color:var(--accent)}.course-header{margin-bottom:36px}.course-title{font-size:2rem;margin:12px 0 8px}.course-description{color:var(--text-muted);max-width:640px;margin-bottom:24px}.lesson-list{list-style:none;display:flex;flex-direction:column;gap:12px}.lesson-row{display:flex;align-items:center;gap:16px;padding:16px 20px;background-color:var(--surface);border:1px solid var(--border);border-radius:var(--radius);transition:border-color .2s,background-color .2s}.lesson-row:hover{border-color:var(--accent);background-color:var(--surface-hover)}.lesson-number{display:flex;align-items:center;justify-content:center;width:32px;height:32px;flex-shrink:0;font-size:.9rem;font-weight:700;color:var(--text-muted);background-color:var(--background);border:1px solid var(--border);border-radius:999px}.lesson-row-title{flex:1 1;font-weight:500}.lesson-duration{color:var(--text-muted);font-size:.88rem}.completed-badge{padding:3px 12px;font-size:.78rem;font-weight:600;color:var(--accent);background-color:var(--accent-soft);border-radius:999px}.certificate{text-align:center;padding:36px 24px;margin-bottom:36px;background:linear-gradient(180deg,var(--accent-soft),rgba(34,197,94,.04));border:1px solid var(--accent);border-radius:var(--radius)}.certificate-emoji{font-size:3rem;line-height:1;margin-bottom:10px}.certificate-title{font-size:1.5rem;color:var(--accent);margin-bottom:6px}.certificate-text{color:var(--text-muted);max-width:460px;margin:0 auto}.lesson-page-title{font-size:1.7rem;margin-bottom:20px}.video-wrapper{aspect-ratio:16/9;background-color:var(--surface);border:1px solid var(--border);border-radius:var(--radius);overflow:hidden;margin-bottom:20px}.video-wrapper iframe{width:100%;height:100%;border:none}.lesson-description{color:var(--text-muted);max-width:720px;margin-bottom:28px}.complete-button{padding:12px 28px;font-size:1rem;font-weight:600;color:#0f1115;background-color:var(--accent);border:1px solid var(--accent);border-radius:var(--radius);cursor:pointer;transition:opacity .2s}.complete-button:hover{opacity:.85}.complete-button.done{color:var(--accent);background-color:var(--accent-soft)}.study-buddy{margin-top:36px;padding:24px;background-color:var(--surface);border:1px solid var(--border);border-radius:var(--radius)}.study-buddy-title{font-size:1.05rem;font-weight:600;margin-bottom:16px}.study-buddy-form{display:flex;gap:10px}.study-buddy-input{flex:1 1;padding:12px 16px;font-size:.95rem;color:var(--text);background-color:var(--background);border:1px solid var(--border);border-radius:var(--radius);outline:none;transition:border-color .2s}.study-buddy-input:focus{border-color:var(--accent)}.study-buddy-input::placeholder{color:var(--text-muted)}.ask-button{padding:12px 24px;font-size:.95rem;font-weight:600;color:#0f1115;background-color:var(--accent);border:1px solid var(--accent);border-radius:var(--radius);cursor:pointer;transition:opacity .2s}.ask-button:hover{opacity:.85}.ask-button:disabled{opacity:.5;cursor:default}.study-buddy-answer{margin-top:16px;padding:16px;color:var(--text);background-color:var(--background);border:1px solid var(--border);border-radius:var(--radius);white-space:pre-wrap}.lesson-nav{display:flex;justify-content:space-between;gap:12px;margin-top:36px}.nav-button{padding:10px 22px;font-size:.95rem;color:var(--text);background-color:var(--surface);border:1px solid var(--border);border-radius:var(--radius);transition:border-color .2s}.nav-button:hover{border-color:var(--accent)}.nav-button.disabled{opacity:.35;pointer-events:none}.empty-message{text-align:center;color:var(--text-muted);padding:48px 0}@media (max-width:900px){.course-grid{grid-template-columns:repeat(2,1fr)}}@media (max-width:600px){.course-grid{grid-template-columns:1fr}.lesson-duration{display:none}}