.lesson-heading { margin-bottom: 24px; max-width: 760px; }
.lesson-heading h1 { font-size: 36px; line-height: 1.15; margin: 10px 0; }
.lesson-heading p { line-height: 1.6; }
.lesson-layout { display: grid; grid-template-columns: minmax(0, 2.4fr) minmax(240px, 1fr); gap: 32px; align-items: start; }
.lesson-layout > * { min-width: 0; }
#lesson-video { display: block; width: 100%; aspect-ratio: 16 / 9; background: #183a3c; object-fit: contain; border-radius: 6px; }
.lesson-progress { display: flex; flex-wrap: wrap; gap: 12px; align-items: center; margin-top: 18px; font-size: 14px; }
.lesson-progress progress { flex: 1; min-width: 80px; height: 10px; accent-color: #167d80; }
.lesson-actions { display: flex; flex-wrap: wrap; align-items: center; gap: 18px; }
.lesson-actions button, #lesson-reload { padding: 10px 16px; border: 1px solid #167d80; background: #167d80; color: white; border-radius: 6px; cursor: pointer; font: inherit; }
.lesson-actions button:disabled { opacity: .5; cursor: default; }
.lesson-chapters { border-left: 1px solid #d3dee5; padding-left: 24px; }
.lesson-chapters h2, .lesson-transcript h2 { font-size: 19px; line-height: 1.3; }
.lesson-chapters ol { list-style: none; padding: 0; margin: 0 0 28px; }
.lesson-chapters button { width: 100%; display: flex; align-items: baseline; gap: 12px; padding: 12px 8px; border: 0; border-bottom: 1px solid #d3dee5; background: transparent; text-align: left; color: #183a3c; cursor: pointer; font: inherit; }
.lesson-chapters button:hover, .lesson-chapters button[aria-current="true"] { background: #e5f3f2; }
.lesson-chapters time { font-variant-numeric: tabular-nums; color: #875330; min-width: 38px; }
.lesson-chapters p, .lesson-transcript p { line-height: 1.7; }
.lesson-transcript { border-top: 1px solid #d3dee5; margin-top: 32px; padding-top: 24px; max-width: 820px; }
.lesson-transcript summary { font-size: 22px; font-weight: 700; cursor: pointer; }
#lesson-status { min-height: 24px; line-height: 1.5; }
.lesson-error { color: #a52943; }
@media (max-width: 820px) { .lesson-layout { grid-template-columns: minmax(0, 1fr); } .lesson-chapters { border-left: 0; padding-left: 0; } }
@media (max-width: 420px) { .lesson-heading h1 { font-size: 30px; } .lesson-progress { font-size: 12px; gap: 8px; } }