*{box-sizing:border-box}
body{font-family:ui-sans-serif,system-ui,-apple-system,Segoe UI,Roboto,Arial,sans-serif;margin:0;background:#0b0e14;color:#e5e7eb}
.app{min-height:100vh;display:flex;flex-direction:column}
.header{padding:18px 22px;border-bottom:1px solid #1c2333;background:#0f1420}
#course-title{font-size:20px;font-weight:700;margin-bottom:12px}
.progress{height:10px;background:#182032;border-radius:999px;overflow:hidden;position:relative}
#progress-fill{height:100%;width:0%;background:#3b82f6;transition:width .3s ease}
#progress-label{position:absolute;right:8px;top:-22px;font-size:12px;color:#9ca3af}
.player{padding:20px;display:flex;flex-direction:column;gap:14px}
video{width:100%;max-height:72vh;background:#000;border:1px solid #1c2333;border-radius:14px}
.controls{display:flex;gap:10px}
button{padding:10px 14px;border-radius:10px;border:1px solid #1c2333;background:#111827;color:#e5e7eb;cursor:pointer}
.hidden{display:none}
.footer{margin-top:auto;padding:12px;color:#9ca3af;font-size:12px;text-align:center;border-top:1px solid #1c2333}