:root {
  --bg: #f5f7fb;
  --card: #ffffff;
  --primary: #4f46e5;
  --primary-dark: #4338ca;
  --text: #1f2937;
  --muted: #6b7280;
  --border: #e5e7eb;
  --danger: #dc2626;
  --ok: #16a34a;
}
* { box-sizing: border-box; }
body {
  margin: 0;
  font-family: "PingFang SC", "Microsoft YaHei", system-ui, sans-serif;
  background: var(--bg);
  color: var(--text);
}
.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 14px 22px;
  background: #fff;
  border-bottom: 1px solid var(--border);
}
.brand { font-weight: 700; font-size: 18px; }
.userbox { font-size: 14px; color: var(--muted); display: flex; gap: 12px; align-items: center; }
.container { max-width: 860px; margin: 24px auto; padding: 0 16px; }

.card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 20px;
  margin-bottom: 16px;
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.04);
}
h2 { margin: 0 0 14px; font-size: 18px; }
label { display: block; font-size: 13px; color: var(--muted); margin: 10px 0 4px; }
input, textarea {
  width: 100%;
  padding: 10px 12px;
  border: 1px solid var(--border);
  border-radius: 8px;
  font-size: 14px;
  font-family: inherit;
}
input:focus, textarea:focus { outline: 2px solid var(--primary); border-color: transparent; }
button {
  cursor: pointer;
  border: none;
  border-radius: 8px;
  padding: 10px 16px;
  font-size: 14px;
  font-weight: 600;
  background: var(--primary);
  color: #fff;
}
button:hover { background: var(--primary-dark); }
button.secondary { background: #eef2ff; color: var(--primary); }
button.ghost { background: transparent; color: var(--muted); }
button.danger { background: #fef2f2; color: var(--danger); }
.row { display: flex; gap: 10px; flex-wrap: wrap; align-items: center; }
.row.end { justify-content: flex-end; }
.hint { font-size: 12px; color: var(--muted); margin-top: 6px; }
.assignment-title { font-size: 16px; font-weight: 600; }
.meta { font-size: 12px; color: var(--muted); margin-top: 4px; }
.actions { display: flex; gap: 8px; margin-top: 12px; }
a.link { color: var(--primary); word-break: break-all; }
video { width: 100%; border-radius: 10px; margin-top: 10px; max-height: 320px; background: #000; }
.progress { height: 8px; background: #e5e7eb; border-radius: 6px; overflow: hidden; margin-top: 8px; }
.progress > i { display: block; height: 100%; width: 0; background: var(--ok); transition: width .2s; }
.toast {
  position: fixed; left: 50%; bottom: 30px; transform: translateX(-50%);
  background: #111827; color: #fff; padding: 10px 18px; border-radius: 10px;
  font-size: 14px; opacity: 0; pointer-events: none; transition: opacity .25s;
}
.toast.show { opacity: 1; }
.center { text-align: center; padding: 40px 0; color: var(--muted); }

/* 登录标签切换 */
.tabs { display: flex; gap: 8px; }
.tab {
  background: #eef2ff; color: var(--muted); flex: 1;
  border-radius: 8px 8px 0 0;
}
.tab.active { background: var(--primary); color: #fff; }

/* 老师视图徽章 */
.badge {
  font-size: 12px; color: var(--primary); background: #eef2ff;
  padding: 4px 10px; border-radius: 999px; white-space: nowrap;
}
select {
  padding: 10px 12px; border: 1px solid var(--border); border-radius: 8px;
  font-size: 14px; font-family: inherit; background: #fff; color: var(--text);
}

/* 评分/评语区块 */
.grade-box {
  margin-top: 14px;
  padding-top: 14px;
  border-top: 1px solid var(--border);
}
.grade-box label { margin-top: 10px; }
.grade-box textarea { resize: vertical; }
.score { color: var(--primary); font-size: 14px; }
.muted { color: var(--muted); font-style: italic; }