:root {
  --bg: #f4f5fb;
  --card: #ffffff;
  --ink: #1c2333;
  --muted: #6b7280;
  --primary: #6366f1;
  --primary-2: #8b5cf6;
  --accent: #22c55e;
  --warn: #f59e0b;
  --danger: #ef4444;
  --radius: 16px;
  --shadow: 0 8px 24px rgba(31, 45, 110, 0.08);
  --border: #e6e8f0;
}

* { box-sizing: border-box; margin: 0; padding: 0; }

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Noto Sans", sans-serif;
  background: var(--bg);
  color: var(--ink);
  min-height: 100vh;
}

a { color: var(--primary); text-decoration: none; }

/* ---------- topbar ---------- */
.topbar {
  position: sticky; top: 0; z-index: 30;
  background: rgba(255,255,255,0.92);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--border);
  display: flex; align-items: center; gap: 16px;
  padding: 10px 22px;
}
.brand { font-weight: 800; font-size: 18px; letter-spacing: -0.3px; }
.brand span { color: var(--primary); }
.topbar nav { display: flex; gap: 4px; flex-wrap: wrap; margin-left: auto; }
.topbar nav a {
  padding: 7px 12px; border-radius: 10px; color: var(--muted);
  font-weight: 600; font-size: 14px; transition: all .15s;
}
.topbar nav a:hover { background: #eef0ff; color: var(--primary); }
.topbar nav a.active { background: var(--primary); color: #fff; }
.topbar .who { display: flex; align-items: center; gap: 12px; }
#student-switch {
  border: 1px solid var(--border); border-radius: 10px; padding: 7px 10px;
  font-size: 14px; background: #fff; color: var(--ink); cursor: pointer;
}
.btn-logout {
  background: none; border: 1px solid var(--border); border-radius: 10px;
  padding: 7px 12px; cursor: pointer; color: var(--muted); font-size: 14px;
}
.btn-logout:hover { border-color: var(--danger); color: var(--danger); }

/* ---------- layout ---------- */
.page { max-width: 1080px; margin: 24px auto; padding: 0 18px; }
.grid2 { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; }
.grid3 { display: grid; grid-template-columns: repeat(3, 1fr); gap: 16px; }
.grid4 { display: grid; grid-template-columns: repeat(4, 1fr); gap: 16px; }
@media (max-width: 820px) {
  .grid2, .grid3, .grid4 { grid-template-columns: 1fr; }
  .topbar { flex-wrap: wrap; }
  .topbar nav { order: 3; width: 100%; overflow-x: auto; }
}

/* ---------- cards ---------- */
.card {
  background: var(--card); border-radius: var(--radius); box-shadow: var(--shadow);
  padding: 20px; border: 1px solid var(--border);
}
.card h2 { font-size: 17px; margin-bottom: 14px; }
.card h3 { font-size: 15px; margin-bottom: 10px; }
.muted { color: var(--muted); font-size: 13px; }
.stat {
  background: var(--card); border-radius: var(--radius); box-shadow: var(--shadow);
  border: 1px solid var(--border); padding: 18px;
}
.stat .num { font-size: 30px; font-weight: 800; }
.stat .lbl { color: var(--muted); font-size: 13px; margin-top: 2px; }

.badge {
  display: inline-block; padding: 3px 10px; border-radius: 999px;
  font-size: 12px; font-weight: 700;
}
.badge.green { background: #dcfce7; color: #15803d; }
.badge.red { background: #fee2e2; color: #b91c1c; }
.badge.amber { background: #fef3c7; color: #b45309; }
.badge.gray { background: #eef0f4; color: #6b7280; }
.badge.indigo { background: #e0e7ff; color: #4338ca; }

/* ---------- student cards ---------- */
.student-card { cursor: pointer; transition: transform .1s; }
.student-card:hover { transform: translateY(-3px); }
.student-avatar {
  width: 54px; height: 54px; border-radius: 16px; display: grid; place-items: center;
  font-size: 28px; color: #fff; margin-bottom: 10px;
}

/* ---------- forms ---------- */
label { display: block; font-size: 13px; font-weight: 600; margin: 10px 0 4px; }
input, select, textarea {
  width: 100%; padding: 10px 12px; border: 1px solid var(--border);
  border-radius: 10px; font-size: 14px; font-family: inherit; background: #fff;
  color: var(--ink);
}
input:focus, select:focus, textarea:focus {
  outline: 2px solid var(--primary); border-color: transparent;
}
textarea { min-height: 90px; resize: vertical; }
.row { display: flex; gap: 10px; flex-wrap: wrap; }
.row > * { flex: 1; min-width: 140px; }

.btn {
  background: var(--primary); color: #fff; border: none; border-radius: 11px;
  padding: 10px 16px; font-size: 14px; font-weight: 700; cursor: pointer;
  transition: filter .15s, transform .05s; display: inline-flex; align-items: center;
  gap: 6px;
}
.btn:hover { filter: brightness(1.07); }
.btn:active { transform: translateY(1px); }
.btn.ghost { background: #fff; color: var(--primary); border: 1px solid var(--primary); }
.btn.small { padding: 6px 11px; font-size: 13px; border-radius: 9px; }
.btn.danger { background: var(--danger); }
.btn.green { background: var(--accent); }
.btn.block { width: 100%; justify-content: center; }

/* ---------- lists ---------- */
.list-item {
  display: flex; align-items: center; gap: 12px; padding: 12px 4px;
  border-bottom: 1px solid var(--border);
}
.list-item:last-child { border-bottom: none; }
.list-item .grow { flex: 1; min-width: 0; }
.list-item .title { font-weight: 600; font-size: 15px; }
.list-item .sub { color: var(--muted); font-size: 12px; margin-top: 2px; }

table { width: 100%; border-collapse: collapse; font-size: 14px; }
th { text-align: left; color: var(--muted); font-size: 12px; text-transform: uppercase;
  letter-spacing: .4px; padding: 8px 6px; border-bottom: 2px solid var(--border); }
td { padding: 9px 6px; border-bottom: 1px solid var(--border); vertical-align: top; }

/* ---------- chat ---------- */
.chat-box { height: 46vh; overflow-y: auto; display: flex; flex-direction: column; gap: 10px; padding: 6px 2px; }
.msg { max-width: 82%; padding: 11px 14px; border-radius: 14px; font-size: 14px; line-height: 1.5; white-space: pre-wrap; }
.msg.user { align-self: flex-end; background: var(--primary); color: #fff; border-bottom-right-radius: 4px; }
.msg.bot { align-self: flex-start; background: #f0f1f8; border-bottom-left-radius: 4px; }
.msg small { display: block; margin-top: 6px; opacity: .6; font-size: 11px; }
.chat-input { display: flex; gap: 8px; margin-top: 12px; }
.chat-input input { flex: 1; }
.typing { color: var(--muted); font-style: italic; }

/* ---------- misc ---------- */
.section-title { font-size: 22px; font-weight: 800; margin: 26px 0 4px; }
.sub-title { color: var(--muted); margin-bottom: 16px; }
.empty { color: var(--muted); text-align: center; padding: 28px 0; font-size: 14px; }
.chip { background: #f0f1f8; border-radius: 999px; padding: 2px 10px; font-size: 12px; font-weight: 600; }
.progress-ring { display: flex; align-items: center; gap: 14px; }
.score-big { font-size: 34px; font-weight: 800; }
.dot { display: inline-block; width: 10px; height: 10px; border-radius: 50%; margin-right: 6px; }
.toast {
  position: fixed; bottom: 20px; left: 50%; transform: translateX(-50%);
  background: var(--ink); color: #fff; padding: 12px 20px; border-radius: 12px;
  font-size: 14px; z-index: 99; box-shadow: var(--shadow); animation: fadeIn .25s;
}
.toast.err { background: var(--danger); }
@keyframes fadeIn { from { opacity: 0; transform: translate(-50%, 8px);} to { opacity: 1; transform: translate(-50%, 0);} }

pre.ocr-text { background: #f7f8fc; border: 1px solid var(--border); border-radius: 12px;
  padding: 14px; font-size: 13px; white-space: pre-wrap; max-height: 320px; overflow-y: auto; }

.login-wrap { max-width: 420px; margin: 8vh auto; padding: 0 18px; }
.login-card { background: var(--card); border-radius: 20px; box-shadow: var(--shadow);
  padding: 30px; border: 1px solid var(--border); }
.login-card h1 { font-size: 24px; font-weight: 800; margin-bottom: 4px; }
.logo-emoji { font-size: 36px; }

.auth-tabs { display: flex; gap: 8px; margin: 16px 0; }
.auth-tabs button { flex: 1; padding: 9px; border-radius: 10px; border: 1px solid var(--border);
  background: #fff; font-weight: 700; cursor: pointer; color: var(--muted); }
.auth-tabs button.on { background: var(--primary); color: #fff; border-color: var(--primary); }