:root {
  --lessons-bg: #121117;
  --lessons-panel: #1b1821;
  --lessons-panel-2: #211d29;
  --lessons-line: #3b3444;
  --lessons-text: #f5f1f8;
  --lessons-muted: #aaa1b2;
  --lessons-accent: #b09bff;
}
* { box-sizing: border-box; }
html, body { min-height: 100%; overflow-x: hidden; }
body { margin: 0; background: radial-gradient(circle at 70% -20%, #2a2142 0, transparent 42%), var(--lessons-bg); color: var(--lessons-text); font: 15px/1.5 "IBM Plex Sans", Arial, sans-serif; }
a { color: inherit; }
.topbar { min-height: 74px; display: flex; align-items: center; gap: 28px; padding: 0 clamp(18px, 4vw, 64px); border-bottom: 1px solid var(--lessons-line); background: rgba(20, 18, 26, .92); position: sticky; top: 0; z-index: 10; backdrop-filter: blur(16px); }
.brand { display: flex; align-items: center; gap: 10px; color: var(--lessons-text); text-decoration: none; font: 10px/1.1 "IBM Plex Mono", monospace; letter-spacing: .08em; text-transform: uppercase; }
.brand b { display: grid; place-items: center; width: 36px; height: 36px; border-radius: 10px; background: var(--lessons-accent); color: #211b2a; font: 700 20px/1 "IBM Plex Sans", sans-serif; }
.app-nav { display: flex; align-items: center; gap: 20px; min-width: 0; margin-right: auto; }
.app-nav > a, .app-nav summary { color: var(--lessons-muted); text-decoration: none; font-size: 13px; white-space: nowrap; cursor: pointer; }
.app-nav > a:hover, .app-nav > a.active, .app-nav summary:hover, .app-nav summary.active { color: var(--lessons-text); }
.app-nav details { position: relative; }
.app-nav summary { list-style: none; }
.app-nav summary::-webkit-details-marker { display: none; }
.app-nav summary::after { content: "⌄"; margin-left: 5px; color: var(--lessons-muted); }
.app-nav details[open] summary::after { content: "⌃"; }
.nav-group-panel { position: absolute; top: calc(100% + 12px); left: 50%; display: grid; min-width: 170px; padding: 8px; transform: translateX(-50%); border: 1px solid var(--lessons-line); border-radius: 12px; background: var(--lessons-panel); box-shadow: 0 18px 50px rgba(0, 0, 0, .35); }
.nav-group-panel a { padding: 9px 10px; border-radius: 7px; color: var(--lessons-muted); text-decoration: none; font-size: 12px; }
.nav-group-panel a:hover, .nav-group-panel a.active { background: rgba(176, 155, 255, .1); color: var(--lessons-text); }
.back { color: var(--lessons-muted); font-size: 13px; text-decoration: none; white-space: nowrap; }
.back:hover { color: var(--lessons-text); }
.lessons-page { width: min(1240px, 100%); margin: 0 auto; padding: clamp(44px, 7vw, 78px) clamp(18px, 4vw, 64px) 90px; }
.lessons-hero { max-width: 690px; margin-bottom: 42px; }
.lessons-hero .eyebrow { display: block; color: var(--lessons-accent); font: 10px "IBM Plex Mono", monospace; letter-spacing: .16em; }
.lessons-hero h1 { margin: 13px 0 16px; color: var(--lessons-text); font-size: clamp(40px, 6vw, 72px); line-height: .96; letter-spacing: -.06em; }
.lessons-hero h1 em { color: var(--lessons-accent); font-style: normal; }
.lessons-hero p { max-width: 570px; margin: 0; color: var(--lessons-muted); font-size: 16px; line-height: 1.65; }
.lessons-grid { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 18px; }
.lesson-card { display: flex; align-items: center; gap: 15px; min-height: 122px; width: 100%; padding: 18px; border: 1px solid var(--lessons-line); border-radius: 16px; background: linear-gradient(145deg, var(--lessons-panel-2), var(--lessons-panel)); color: var(--lessons-text); text-align: left; box-shadow: 0 18px 45px rgba(0, 0, 0, .18); cursor: pointer; transition: border-color .18s ease, transform .18s ease, background .18s ease; }
.lesson-card:hover, .lesson-card:focus-visible { border-color: var(--lessons-accent); background: #29223a; transform: translateY(-2px); }
.lesson-card-art { display: grid; place-items: center; flex: 0 0 62px; aspect-ratio: 1; border-radius: 14px; background: linear-gradient(145deg, #7d61e1, #a997f0); color: #211b2a; font-size: 21px; }
.lesson-card-copy { display: grid; gap: 5px; min-width: 0; }
.lesson-card-copy strong { overflow-wrap: anywhere; font-size: 15px; line-height: 1.3; }
.lesson-card-copy small { color: var(--lessons-muted); font-size: 12px; }
.lessons-empty { grid-column: 1 / -1; padding: 66px 24px; border: 1px dashed var(--lessons-line); border-radius: 16px; background: rgba(255, 255, 255, .02); color: var(--lessons-muted); text-align: center; }
.lessons-empty strong { display: block; color: var(--lessons-text); font-size: 22px; }
.lessons-empty p { margin: 8px 0 0; }
.lesson-launcher { display: inline-flex; align-items: center; justify-content: center; margin: 20px 0 0; padding: 12px 18px; border: 1px solid var(--lessons-accent); border-radius: 999px; background: var(--lessons-accent); color: #211b2a; font: 700 13px "IBM Plex Sans", sans-serif; box-shadow: 0 12px 30px rgba(33, 25, 57, .42); cursor: pointer; }
.lesson-launcher:hover, .lesson-launcher:focus-visible { background: #c5b7ff; }
.lessons-dialog { width: min(720px, calc(100vw - 32px)); max-width: 720px; max-height: min(90vh, 720px); margin: auto; padding: 0; border: 1px solid var(--lessons-line); border-radius: 18px; background: var(--lessons-panel); color: var(--lessons-text); box-shadow: 0 28px 90px rgba(0, 0, 0, .5); overflow: hidden; }
.lessons-dialog::backdrop { background: rgba(5, 4, 8, .76); backdrop-filter: blur(4px); }
.lessons-dialog-inner { position: relative; max-height: min(90vh, 720px); overflow: auto; padding: 30px; }
.lessons-dialog .eyebrow { color: var(--lessons-accent); font: 10px "IBM Plex Mono", monospace; letter-spacing: .15em; }
.lessons-dialog h2 { margin: 9px 44px 22px 0; font-size: clamp(25px, 4vw, 36px); line-height: 1; letter-spacing: -.045em; }
.lessons-close { position: absolute; top: 15px; right: 15px; width: 34px; height: 34px; border: 1px solid var(--lessons-line); border-radius: 50%; background: transparent; color: var(--lessons-text); font-size: 22px; line-height: 1; cursor: pointer; }
.lessons-close:hover, .lessons-close:focus-visible { border-color: var(--lessons-accent); background: rgba(176, 155, 255, .1); }
.lesson-close-question { padding: 18px; border: 1px solid var(--lessons-line); border-radius: 13px; background: rgba(176, 155, 255, .07); }
.lesson-close-question[hidden] { display: none; }
.lesson-close-question strong { display: block; font-size: 17px; }
.lesson-close-question p { margin: 7px 0 16px; color: var(--lessons-muted); font-size: 13px; line-height: 1.5; }
.lesson-close-question > div { display: flex; flex-wrap: wrap; gap: 8px; }
.lesson-close-choice, .lesson-close-cancel { min-height: 38px; padding: 9px 12px; border: 1px solid var(--lessons-accent); border-radius: 9px; background: var(--lessons-accent); color: #211b2a; font: 700 12px "IBM Plex Sans", sans-serif; cursor: pointer; }
.lesson-close-choice-muted, .lesson-close-cancel { border-color: var(--lessons-line); background: transparent; color: var(--lessons-text); }
.lesson-close-cancel { margin-top: 14px; border: 0; padding-left: 0; color: var(--lessons-accent); }
.lesson-dialog-list { display: grid; gap: 10px; }
.lesson-dialog-item { display: flex; align-items: center; gap: 13px; width: 100%; padding: 14px; border: 1px solid var(--lessons-line); border-radius: 12px; background: rgba(255, 255, 255, .025); color: var(--lessons-text); text-align: left; cursor: pointer; }
.lesson-dialog-item:hover, .lesson-dialog-item:focus-visible { border-color: var(--lessons-accent); background: rgba(176, 155, 255, .1); }
.lesson-dialog-item > span:last-child { display: grid; gap: 4px; min-width: 0; }
.lesson-dialog-item strong { overflow-wrap: anywhere; }
.lesson-dialog-item small { color: var(--lessons-muted); }
.lesson-play { display: grid; place-items: center; flex: 0 0 38px; height: 38px; border-radius: 50%; background: var(--lessons-accent); color: #211b2a; font-size: 13px; }
.lesson-player[hidden], .lesson-dialog-list[hidden] { display: none; }
.lesson-player iframe { display: block; width: 100%; aspect-ratio: 16 / 9; border: 0; border-radius: 11px; background: #09080b; }
.lesson-back { margin: 0 0 12px; padding: 0; border: 0; background: transparent; color: var(--lessons-accent); font: 700 13px "IBM Plex Sans", sans-serif; cursor: pointer; }
@media (max-width: 900px) { .lessons-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); } }
@media (max-width: 700px) { .topbar { flex-wrap: wrap; gap: 14px; padding: 14px 16px; } .app-nav { order: 3; width: 100%; overflow-x: auto; gap: 18px; padding-bottom: 2px; } .back { margin-left: auto; font-size: 12px; } }
@media (max-width: 560px) { .lessons-page { padding: 40px 16px 76px; } .lessons-grid { grid-template-columns: 1fr; } .lesson-launcher { margin-top: 16px; } .lessons-dialog { width: calc(100vw - 20px); border-radius: 15px; } .lessons-dialog-inner { padding: 24px 16px 18px; } }
@media (prefers-reduced-motion: reduce) { .lesson-card { transition: none; } }