:root {
  --bg: #f3f6fb;
  --panel: #ffffff;
  --text: #18212f;
  --muted: #64748b;
  --primary: #2563eb;
  --primary-dark: #1d4ed8;
  --success: #059669;
  --danger: #dc2626;
  --warning: #d97706;
  --border: #dbe2ea;
  --shadow: 0 10px 30px rgba(15, 23, 42, .08);
}

* { box-sizing: border-box; }
html, body { margin: 0; min-height: 100%; }
body {
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif;
  background: radial-gradient(circle at top left, #e0edff 0, var(--bg) 38%);
}

.topbar {
  min-height: 64px;
  padding: 14px max(20px, env(safe-area-inset-left));
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  background: rgba(255,255,255,.92);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 10;
}
.brand { display: flex; align-items: center; gap: 10px; font-weight: 750; font-size: 19px; }
.brand-mark {
  width: 34px; height: 34px; border-radius: 9px; color: white;
  display: grid; place-items: center; background: linear-gradient(135deg,#2563eb,#7c3aed);
}
.toolbar { display: flex; align-items: center; justify-content: flex-end; gap: 8px; flex-wrap: wrap; }

.page { max-width: 1280px; margin: 24px auto 60px; padding: 0 20px; }
.login-wrap { min-height: calc(100vh - 80px); display: grid; place-items: center; }
.login-card, .panel {
  width: min(430px, calc(100vw - 32px));
  background: var(--panel); border: 1px solid var(--border);
  border-radius: 16px; padding: 28px; box-shadow: var(--shadow);
}
.panel { width: 100%; margin-bottom: 18px; }
.title { margin: 0 0 6px; font-size: 24px; }
.subtitle { margin: 0 0 22px; color: var(--muted); line-height: 1.6; }

label { display: block; margin: 14px 0 6px; font-size: 14px; font-weight: 650; }
input, select {
  width: 100%; height: 42px; border: 1px solid var(--border); border-radius: 8px;
  padding: 0 12px; font-size: 15px; color: var(--text); background: #fff; outline: none;
}
input:focus, select:focus { border-color: var(--primary); box-shadow: 0 0 0 3px rgba(37,99,235,.13); }
button {
  height: 38px; border: 0; border-radius: 8px; padding: 0 14px; font-size: 14px;
  cursor: pointer; color: white; background: var(--primary); transition: .15s;
}
button:hover:not(:disabled) { background: var(--primary-dark); transform: translateY(-1px); }
button:disabled { cursor: not-allowed; opacity: .5; transform: none; }
button.full { width: 100%; height: 42px; margin-top: 18px; font-weight: 650; }
button.ghost { color: var(--text); background: #eef2f7; }
button.success { background: var(--success); }
button.danger { background: var(--danger); }
button.warning { background: var(--warning); }
button.small { height: 30px; padding: 0 8px; font-size: 12px; white-space: nowrap; }

.hidden { display: none !important; }
.notice {
  min-height: 20px; margin-top: 12px; font-size: 14px; color: var(--danger);
  text-align: center; white-space: pre-wrap;
}
.hint { color: var(--muted); font-size: 13px; line-height: 1.6; }
.status-row { display: flex; gap: 8px; flex-wrap: wrap; align-items: center; }
.chip {
  display: inline-flex; align-items: center; min-height: 28px; padding: 3px 10px;
  border-radius: 999px; background: #eef2f7; color: #334155; font-size: 13px; white-space: nowrap;
}
.chip.active { background: #dcfce7; color: #166534; }
.chip.locked { background: #ffedd5; color: #9a3412; }
.chip.leader { background: #dbeafe; color: #1e40af; }
.chip.member { background: #f1f5f9; color: #475569; }
.chip.full { background: #fee2e2; color: #991b1b; }
.section-head { display: flex; justify-content: space-between; align-items: center; gap: 14px; margin-bottom: 14px; flex-wrap: wrap; }
h1,h2,h3 { line-height: 1.25; }
h2 { margin: 0; font-size: 20px; }
h3 { margin: 0; font-size: 17px; }
.class-tabs { display: flex; gap: 8px; flex-wrap: wrap; }
.class-tab {
  height: 34px; padding: 0 13px; border-radius: 8px; background: #fff;
  border: 1px solid var(--border); color: #334155;
}
.class-tab.active { border-color: transparent; background: var(--primary); color: #fff; }
.class-panel { margin-bottom: 14px; }
.class-panel .status-row { margin-top: 14px; }

.admin-tabs {
  display: flex; gap: 6px; align-items: center; overflow-x: auto;
  padding: 7px; margin: 0 0 16px; background: rgba(255,255,255,.94);
  border: 1px solid var(--border); border-radius: 14px; box-shadow: 0 5px 16px rgba(15,23,42,.05);
}
.admin-tab {
  flex: 1 0 auto; min-width: 118px; height: 40px; border-radius: 10px;
  background: transparent; color: var(--muted); font-size: 14px; font-weight: 650;
  white-space: nowrap; transition: color .15s, background-color .15s, transform .15s;
}
.admin-tab:hover:not(:disabled) { background: #eef2f7; color: var(--text); transform: none; }
.admin-tab.active { background: var(--primary); color: #fff; }
.admin-tab.active:hover:not(:disabled) { background: var(--primary-dark); color: #fff; }
.tab-panel { margin-bottom: 0; }
.statistics { margin: 0 0 20px; }
.create-group-line { margin-bottom: 24px; }
.groups-head { margin-top: 4px; }
.import-label {
  display: inline-flex; align-items: center; height: 38px; padding: 0 14px;
  border: 0; border-radius: 8px; background: #eef2f7; color: var(--text);
  font-size: 14px; font-weight: 500; line-height: 1; cursor: pointer; transition: .15s;
}
.import-label:hover { background: #e2e8f0; }
.settings-divider { height: 1px; margin: 26px 0 22px; background: var(--border); }
.settings-password-line { margin-top: 14px; }
.student-search { max-width: 560px; }
.student-search + .account-password-form { margin-top: 14px; }
.account-password-form {
  display: grid; grid-template-columns: max-content minmax(220px, 340px);
  gap: 12px 14px; align-items: center; max-width: 560px;
}
.account-password-form .field-label { color: var(--muted); font-size: 14px; font-weight: 600; }
.account-password-form button { grid-column: 2; justify-self: start; }

.grid {
  display: grid; grid-template-columns: repeat(auto-fill,minmax(290px,1fr)); gap: 16px;
}
.group-card {
  background: var(--panel); border: 1px solid var(--border); border-radius: 14px;
  padding: 15px; box-shadow: 0 5px 16px rgba(15,23,42,.05); align-self: start;
}
.group-card.own { border-color: var(--primary); box-shadow: 0 8px 24px rgba(37,99,235,.14); }
.group-top { display: flex; justify-content: space-between; align-items: center; gap: 8px; margin-bottom: 12px; }
.group-title { font-weight: 750; overflow-wrap: anywhere; }
.member-list { margin: 0 0 12px; padding: 0; list-style: none; }
.member-list li {
  min-height: 42px; padding: 7px 0; border-top: 1px solid #edf2f7;
  display: flex; align-items: center; justify-content: space-between; gap: 8px;
}
.member-list li:first-child { border-top: 0; }
.member-name { min-width: 0; overflow-wrap: anywhere; }
.member-actions { display: flex; gap: 5px; flex-shrink: 0; }
.empty { color: var(--muted); text-align: center; padding: 24px 0; }
.form-line { display: flex; gap: 8px; align-items: center; }
.form-line input, .form-line select { flex: 1; min-width: 0; }
.actions { display: flex; gap: 8px; flex-wrap: wrap; }
.statistics { display: grid; grid-template-columns: repeat(3,1fr); gap: 10px; margin-bottom: 16px; }
.statistic { background: #fff; border: 1px solid var(--border); border-radius: 12px; padding: 13px; }
.statistic strong { display: block; font-size: 24px; }
.statistic span { color: var(--muted); font-size: 13px; }
.two-col { display: grid; grid-template-columns: 340px 1fr; gap: 18px; align-items: start; }
.identity { display: grid; grid-template-columns: auto 1fr; gap: 6px 14px; margin: 14px 0 18px; }
.identity span:first-child { color: var(--muted); }

.modal-mask {
  position: fixed; inset: 0; z-index: 100; display: grid; place-items: center;
  background: rgba(15,23,42,.55); padding: 18px; backdrop-filter: blur(3px);
}
.modal {
  width: min(460px,100%); background: #fff; border-radius: 15px; padding: 26px; box-shadow: var(--shadow);
}
.modal-actions { display: grid; grid-template-columns: 1fr 1fr; gap: 10px; margin-top: 20px; }
.toast {
  position: fixed; left: 50%; bottom: 30px; transform: translateX(-50%) translateY(20px);
  max-width: min(640px, calc(100vw - 32px)); padding: 13px 18px; border-radius: 10px;
  background: #0f172a; color: #fff; box-shadow: var(--shadow); z-index: 200; opacity: 0;
  transition: .2s; pointer-events: none; font-size: 14px; line-height: 1.5;
}
.toast.show { opacity: 1; transform: translateX(-50%) translateY(0); }
.toast.error { background: #b91c1c; }
.loading { color: var(--muted); text-align: center; padding: 40px; }

@media (max-width: 800px) {
  .page { margin-top: 14px; }
  .two-col { grid-template-columns: 1fr; }
  .statistics { grid-template-columns: 1fr; }
  .topbar { padding: 12px 14px; }
  .brand span { display: none; }
  .group-card { padding: 13px; }
  .member-actions button { padding: 0 6px; }
  .admin-tabs { gap: 5px; padding: 6px; margin-bottom: 13px; }
  .admin-tab { min-width: 96px; height: 38px; font-size: 13px; }
  .class-panel, .import-label, .create-group-line { margin-bottom: 14px; }
  .form-line { flex-direction: column; align-items: stretch; }
  .account-password-form { grid-template-columns: 1fr; }
  .account-password-form button { grid-column: auto; justify-self: stretch; }
  .form-line button, .form-line span { width: 100%; text-align: center; }
  .form-line span { height: auto; color: var(--muted); font-size: 13px; }
}