:root {
  --blue: #2563EB;
  --blue-dark: #1D4ED8;
  --blue-tint: #EFF4FF;
  --ink: #18181B;
  --ink-2: #3F3F46;
  --slate: #71717A;
  --muted: #A1A1AA;
  --bg: #FFFFFF;
  --surface: #F7F8FA;
  --surface-2: #F4F4F5;
  --border: #EAECEF;
  --amber: #D97706;
  --amber-tint: #FEF6E7;
  --amber-deep: #92400E;
  --green: #16A34A;
  --green-tint: #ECFDF3;
  --green-deep: #166534;
  --r-sm: 6px;
  --r: 8px;
  --r-lg: 10px;
  --r-xl: 12px;
  --shadow: 0 8px 24px rgba(15,15,15,.08);
  --font: "Noto Sans SC", "PingFang SC", "Microsoft YaHei", -apple-system, system-ui, sans-serif;
}

* { margin: 0; padding: 0; box-sizing: border-box; }
html, body { height: 100%; }
body {
  font-family: var(--font);
  color: var(--ink);
  background: var(--bg);
  font-size: 14px;
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
}

.app { display: flex; min-height: 100vh; }

/* ---------- Sidebar ---------- */
.sidebar {
  width: 220px;
  flex: 0 0 220px;
  background: #fff;
  border-right: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  padding: 16px;
  position: sticky;
  top: 0;
  height: 100vh;
}
.brand { font-size: 16px; font-weight: 700; color: var(--ink); }
.brand-sub { font-size: 12px; color: var(--muted); margin-top: 4px; }
.nav-sep { height: 1px; background: var(--border); margin: 16px 0 8px; }
.nav-item {
  display: block;
  padding: 10px 12px;
  border-radius: var(--r-sm);
  color: var(--ink-2);
  font-size: 14px;
  cursor: pointer;
  text-decoration: none;
  user-select: none;
}
.nav-item:hover { background: var(--surface); }
.nav-item.active { background: var(--blue-tint); color: var(--blue); font-weight: 600; }
.nav-spacer { flex: 1; }
.nav-bottom-sep { height: 1px; background: var(--border); margin: 8px 0; }
.nav-item.muted { color: var(--slate); font-size: 13px; }

/* ---------- Content ---------- */
.content {
  flex: 1;
  min-width: 0;
  padding: 32px;
  max-width: 1440px;
}
.header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  margin-bottom: 24px;
}
.header-title { font-size: 26px; font-weight: 700; }
.header-sub { font-size: 13px; color: var(--slate); margin-top: 6px; }
.header-actions { display: flex; gap: 12px; align-items: center; }

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  border: none;
  border-radius: var(--r);
  padding: 9px 14px;
  font-size: 14px;
  font-family: var(--font);
  font-weight: 500;
  cursor: pointer;
  white-space: nowrap;
}
.btn-primary { background: var(--blue); color: #fff; }
.btn-primary:hover { background: var(--blue-dark); }
.btn-ghost { background: var(--surface-2); color: var(--ink); }
.btn-ghost:hover { background: #e9e9ec; }
.btn-outline { background: #fff; color: var(--ink-2); border: 1px solid var(--border); }
.btn-outline:hover { background: var(--surface); }
.btn-sm { padding: 7px 12px; font-size: 13px; }
.btn-link { background: none; color: var(--blue); padding: 4px 0; font-size: 12px; }

/* Grid */
.grid { display: grid; gap: 24px; }
.cols-2 { grid-template-columns: 1fr 360px; align-items: start; }
.col { display: flex; flex-direction: column; gap: 24px; }

/* Section */
.section { display: flex; flex-direction: column; gap: 14px; }
.section-head { display: flex; align-items: center; gap: 10px; }
.section-title { font-size: 18px; font-weight: 700; }
.count { background: var(--blue-tint); color: var(--blue); font-size: 12px; font-weight: 600; padding: 4px 10px; border-radius: 999px; }
.count.amber { background: var(--amber-tint); color: var(--amber); }
.count.green { background: var(--green-tint); color: var(--green); }

/* Cards */
.card {
  background: #fff;
  border: 1px solid var(--border);
  border-radius: var(--r-lg);
  padding: 16px;
}
.card.surface { background: var(--surface); border: none; }
.card.tint-blue { background: var(--blue-tint); border: none; }
.card.tint-amber { background: var(--amber-tint); border: none; }

/* Tabs */
.tabs { display: inline-flex; gap: 4px; }
.tab {
  padding: 6px 14px;
  border-radius: 999px;
  background: var(--surface-2);
  color: var(--ink-2);
  font-size: 13px;
  cursor: pointer;
  border: none;
  font-family: var(--font);
}
.tab.active { background: var(--ink); color: #fff; }

/* Course timeline */
.course {
  display: flex;
  align-items: center;
  gap: 16px;
  background: var(--surface);
  border-radius: var(--r-lg);
  padding: 16px;
}
.course.upcoming { background: #fff; border: 1px solid var(--border); flex-direction: column; align-items: stretch; gap: 10px; }
.course-top { display: flex; align-items: center; gap: 16px; }
.course-time { display: flex; flex-direction: column; gap: 2px; width: 56px; }
.course-time .t { font-size: 16px; font-weight: 700; }
.course-time .d { font-size: 11px; color: var(--muted); }
.course-info { flex: 1; display: flex; flex-direction: column; gap: 4px; }
.course-meta { display: flex; align-items: center; gap: 8px; flex-wrap: wrap; }
.tag { background: #fff; color: var(--blue); font-size: 12px; font-weight: 500; padding: 3px 8px; border-radius: var(--r-sm); }
.tag.tint { background: var(--blue-tint); }
.tag.gray { background: var(--surface-2); color: var(--slate); }
.tag.green { background: var(--green-tint); color: var(--green); }
.tag.amber { background: var(--amber-tint); color: var(--amber); }
.course-chap { font-size: 15px; font-weight: 600; }
.course-actions { display: flex; gap: 8px; align-items: center; }
.quick-actions { display: flex; gap: 8px; flex-wrap: wrap; }

/* Task cards */
.task {
  display: flex;
  align-items: center;
  gap: 14px;
  background: #fff;
  border: 1px solid var(--border);
  border-radius: var(--r-lg);
  padding: 16px;
}
.task-type {
  width: 40px; height: 40px;
  flex: 0 0 40px;
  border-radius: var(--r);
  display: flex; align-items: center; justify-content: center;
  font-size: 11px; font-weight: 600;
}
.task-type.blue { background: var(--blue-tint); color: var(--blue); }
.task-type.gray { background: var(--surface-2); color: var(--slate); }
.task-type.green { background: var(--green-tint); color: var(--green); }
.task-type.amber { background: var(--amber-tint); color: var(--amber); }
.task-info { flex: 1; display: flex; flex-direction: column; gap: 3px; min-width: 0; }
.task-name { font-size: 14px; font-weight: 500; }
.task-meta { font-size: 12px; color: var(--slate); }
.task-actions { display: flex; gap: 8px; }

/* Overview stat chips */
.stats { display: grid; grid-template-columns: repeat(2,1fr); gap: 12px; }
.stat { background: var(--surface); border-radius: var(--r-lg); padding: 14px; display: flex; flex-direction: column; gap: 4px; }
.stat .n { font-size: 24px; font-weight: 700; }
.stat .l { font-size: 12px; color: var(--slate); }

/* AI suggestion */
.suggest { background: var(--blue-tint); border-radius: var(--r); padding: 14px; display: flex; flex-direction: column; gap: 10px; }
.suggest.amber { background: var(--amber-tint); }
.suggest p { font-size: 13px; line-height: 1.5; color: #1E3A8A; }
.suggest.amber p { color: var(--amber-deep); }

/* Lesson plan grid */
.plan-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; }
.plan { background: var(--surface); border-radius: var(--r-lg); padding: 16px; display: flex; flex-direction: column; gap: 8px; }
.plan h4 { font-size: 14px; font-weight: 600; }
.plan p { font-size: 13px; color: var(--ink-2); line-height: 1.6; }

/* Student card */
.student-card {
  border: 1px solid var(--border);
  border-radius: var(--r-xl);
  padding: 20px;
  display: flex;
  flex-direction: column;
  gap: 14px;
}
.student-head { display: flex; align-items: center; justify-content: space-between; }
.student-name { font-size: 20px; font-weight: 700; }
.student-class { font-size: 12px; color: var(--slate); }
.tags { display: flex; gap: 6px; flex-wrap: wrap; }
.ai-summary { background: var(--surface); border-radius: var(--r); padding: 14px; display: flex; flex-direction: column; gap: 6px; }
.ai-summary .h { font-size: 13px; font-weight: 600; color: var(--blue); }
.ai-summary p { font-size: 13px; color: var(--ink-2); line-height: 1.6; }
.row-actions { display: flex; gap: 10px; flex-wrap: wrap; }

/* Homework */
.hw-card {
  display: flex; align-items: center; gap: 16px;
  background: #fff; border: 1px solid var(--border); border-radius: var(--r-lg); padding: 16px;
}

/* AI assistant */
.chips { display: flex; gap: 10px; flex-wrap: wrap; }
.chip { background: var(--blue-tint); color: var(--blue); font-size: 12px; font-weight: 500; padding: 6px 12px; border-radius: 999px; display: inline-flex; align-items: center; gap: 6px; }
.quick-entries { display: flex; gap: 10px; flex-wrap: wrap; }
.entry { background: var(--surface-2); border-radius: var(--r); padding: 10px 14px; font-size: 13px; font-weight: 500; cursor: pointer; border: none; font-family: var(--font); color: var(--ink); }
.entry:hover { background: #e9e9ec; }
.chat { background: var(--surface); border-radius: var(--r-xl); padding: 20px; display: flex; flex-direction: column; gap: 14px; }
.bubble { background: #fff; border-radius: var(--r-lg); padding: 14px; display: flex; flex-direction: column; gap: 6px; }
.bubble .who { font-size: 12px; font-weight: 600; color: var(--blue); }
.bubble p { font-size: 13px; color: var(--ink-2); line-height: 1.6; }
.bubble.user { background: var(--blue); align-self: flex-end; max-width: 360px; }
.bubble.user .who { color: #fff; opacity: .85; }
.bubble.user p { color: #fff; }
.input-bar { display: flex; gap: 10px; align-items: center; background: #fff; border: 1px solid var(--border); border-radius: var(--r-xl); padding: 10px; }
.input-bar input { flex: 1; border: none; outline: none; font-size: 14px; font-family: var(--font); color: var(--ink); background: transparent; }

/* FAB */
.fab {
  position: fixed;
  right: 32px; bottom: 32px;
  width: 56px; height: 56px;
  border-radius: 999px;
  background: var(--blue);
  color: #fff;
  font-size: 30px;
  border: none;
  cursor: pointer;
  box-shadow: var(--shadow);
  display: flex; align-items: center; justify-content: center;
  z-index: 50;
}
.fab-menu {
  position: fixed;
  right: 32px; bottom: 100px;
  background: #fff;
  border: 1px solid var(--border);
  border-radius: var(--r-lg);
  box-shadow: var(--shadow);
  padding: 8px;
  display: none;
  flex-direction: column;
  gap: 2px;
  z-index: 50;
  width: 160px;
}
.fab-menu.open { display: flex; }
.fab-menu button {
  text-align: left; border: none; background: none; padding: 10px 12px;
  border-radius: var(--r-sm); cursor: pointer; font-size: 14px; color: var(--ink); font-family: var(--font);
}
.fab-menu button:hover { background: var(--surface); }

/* Toast */
.toast {
  position: fixed; left: 50%; bottom: 40px; transform: translateX(-50%);
  background: var(--ink); color: #fff; padding: 10px 18px; border-radius: 999px;
  font-size: 13px; opacity: 0; transition: opacity .2s, bottom .2s; z-index: 100; pointer-events: none;
}
.toast.show { opacity: 1; bottom: 56px; }

/* Empty / placeholder */
.placeholder { border: 1px dashed var(--border); border-radius: var(--r-lg); padding: 40px; text-align: center; color: var(--slate); font-size: 14px; }

.view { display: none; }
.view.active { display: block; }
.hidden { display: none !important; }
@media (max-width: 1100px) {
  .cols-2 { grid-template-columns: 1fr; }
  .plan-grid { grid-template-columns: 1fr; }
  .stats { grid-template-columns: 1fr 1fr; }
}