* { box-sizing: border-box; }
body { font-family: system-ui, -apple-system, Segoe UI, Roboto, Arial, sans-serif; margin: 0; background: #f7f7f9; color: #222; }
.site-header { background: #0b5; color: #fff; padding: 12px 20px; }
.site-header h1 { margin: 0 0 8px; font-size: 20px; }
.main-nav a { margin-right: 12px; color: #fff; text-decoration: none; font-weight: 600; }
.main-nav a.locked { opacity: .8; }
.main-nav a.disabled { pointer-events: none; opacity: .6; }
.container { max-width: 960px; margin: 24px auto; padding: 0 16px; }
.hero { background: #fff; padding: 20px; border-radius: 8px; box-shadow: 0 1px 4px rgba(0,0,0,.08); }
.announcements { margin-top: 16px; background: #fff; padding: 16px; border-radius: 8px; box-shadow: 0 1px 4px rgba(0,0,0,.08); }
.auth-container { max-width: 720px; margin: 32px auto; background: #fff; padding: 24px; border-radius: 8px; box-shadow: 0 1px 4px rgba(0,0,0,.08); }
.auth-panels { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; }
.panel { background: #fdfdfd; padding: 16px; border: 1px solid #eee; border-radius: 6px; }
label { display: block; margin-top: 8px; font-size: 14px; }
input { width: 100%; padding: 10px; margin-top: 4px; border: 1px solid #ccc; border-radius: 4px; }
.alert { background: #fee; border: 1px solid #fbb; color: #a00; padding: 10px; border-radius: 4px; margin-bottom: 10px; }
.btn { background: #06c; color: #fff; border: none; padding: 10px 14px; border-radius: 4px; cursor: pointer; margin-right: 8px; }
.btn[disabled] { background: #9bb; cursor: not-allowed; }
.grid.two { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; }
.grid.three { display: grid; grid-template-columns: repeat(3, 1fr); gap: 16px; }
.card { background: #fff; padding: 16px; border-radius: 8px; box-shadow: 0 1px 4px rgba(0,0,0,.08); }
.disabled { color: #777; }
.notice { background: #eef; border: 1px solid #bbf; color: #114; padding: 10px; border-radius: 4px; }
.classroom { display: grid; grid-template-columns: 2fr 1fr; grid-template-rows: auto 1fr; gap: 12px; }
.classroom .docs { background: #fff; padding: 12px; border-radius: 8px; min-height: 300px; }
.classroom .video { background: #000; color: #fff; padding: 12px; border-radius: 8px; min-height: 300px; }
.classroom .controls { grid-column: 1 / -1; background: #fff; padding: 12px; border-radius: 8px; }