:root{--navy: #1b2a4a;--teal: #0e7c7b;--teal-light: #eaf3f3;--grey: #595959;--border: #d9d9d9;--bg: #fafafa;font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Arial,sans-serif}*{box-sizing:border-box}body{margin:0;background:var(--bg);color:#1a1a1a}button{cursor:pointer;font-family:inherit;font-size:13px;border:.5px solid var(--border);background:#fff;border-radius:8px;padding:8px 14px}button:hover{background:#f3f3f3}input,select{font-family:inherit;font-size:14px;padding:8px 10px;border:.5px solid var(--border);border-radius:8px;width:100%}.app-shell{max-width:880px;margin:0 auto;padding:24px 20px 80px}.card{background:#fff;border:.5px solid var(--border);border-radius:12px;padding:16px 18px}.tier-badge{font-size:11px;padding:3px 10px;border-radius:8px;background:var(--teal-light);color:var(--teal);white-space:nowrap}.lesson-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(200px,1fr));gap:10px}.lesson-card{cursor:pointer;transition:opacity .15s}.lesson-card.locked{opacity:.5;cursor:default}.nav-tabs{display:flex;gap:6px;border-bottom:.5px solid var(--border);margin-bottom:20px}.nav-tab{border:none;border-bottom:2px solid transparent;border-radius:0;background:none;padding:8px 4px;font-size:14px;color:var(--grey)}.nav-tab.active{border-bottom-color:var(--navy);color:var(--navy);font-weight:600}.video-frame{background:#1a1a1a;border-radius:12px;aspect-ratio:16/9;display:flex;align-items:center;justify-content:center;flex-direction:column;gap:8px;color:#aaa;position:relative;overflow:hidden}.video-frame iframe{position:absolute;top:0;right:0;bottom:0;left:0;width:100%;height:100%;border:0}