/* Khai báo màu cho Giao diện Tối (Mặc định) */
:root {
  --bg: #0f172a;
  --surface: rgba(255, 255, 255, 0.06);
  --ink: #f8fafc;
  --muted: #94a3b8;
  --accent: #3b82f6;
  --good: #10b981;
  --bad: #ef4444;
  --border: rgba(255, 255, 255, 0.18);
  --input-bg: rgba(0, 0, 0, 0.2);
}

/* Ghi đè màu khi bật Giao diện Sáng (Light mode) */
body.light-mode {
  --bg: #eef2f7;
  --surface: rgba(255, 255, 255, 0.8);
  --ink: #0f172a;
  --muted: #475569;
  --border: rgba(15, 23, 42, 0.12);
  --input-bg: rgba(255, 255, 255, 0.9);
}

body {
  background-color: var(--bg) !important;
  background-image: none !important;
  color: var(--ink);
  font-family:
    system-ui,
    -apple-system,
    sans-serif;
  margin: 0;
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: flex-start;
  padding: 40px 20px;
  box-sizing: border-box;
  transition:
    background-color 0.3s ease,
    color 0.3s ease;
}

.container {
  width: 100%;
  max-width: 1000px;
  background: var(--surface);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border: 1px solid var(--border);
  border-radius: 20px;
  padding: 30px;
  box-shadow: 0 16px 40px 0 rgba(0, 0, 0, 0.15);
}

h2,
h3,
h4 {
  margin-top: 0;
  margin-bottom: 20px;
  color: var(--ink);
}

input,
select,
textarea,
button {
  width: 100%;
  padding: 12px 15px;
  margin-bottom: 15px;
  border-radius: 10px;
  border: 1px solid var(--border);
  background: var(--input-bg);
  color: var(--ink);
  font-size: 1rem;
  outline: none;
  box-sizing: border-box;
  font-family: inherit;
  transition:
    background-color 0.3s ease,
    border-color 0.3s ease;
}

input:focus,
select:focus,
textarea:focus {
  border-color: var(--accent);
}
textarea {
  resize: vertical;
  min-height: 100px;
}

button {
  background: var(--accent);
  border: none;
  font-weight: bold;
  cursor: pointer;
  transition: 0.2s;
  color: #fff;
}
button:hover {
  background: #2563eb;
  transform: translateY(-2px);
}
button:disabled {
  background: #475569;
  cursor: not-allowed;
  transform: none;
}

.hidden {
  display: none !important;
}
.header-bar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  border-bottom: 1px solid var(--border);
  padding-bottom: 15px;
  margin-bottom: 20px;
}
.btn-logout {
  width: auto;
  background: transparent;
  border: 1px solid var(--bad);
  color: var(--bad);
  padding: 8px 15px;
  margin: 0;
}
.btn-logout:hover {
  background: var(--bad);
  color: #fff;
}

/* Tabs */
.tabs {
  display: flex;
  gap: 10px;
  margin-bottom: 20px;
  border-bottom: 1px solid var(--border);
  padding-bottom: 10px;
}
.tab-btn {
  background: transparent;
  border: none;
  color: var(--muted);
  font-weight: bold;
  padding: 10px 20px;
  margin: 0;
  width: auto;
  cursor: pointer;
  border-radius: 8px;
}
.tab-btn.active {
  background: var(--accent);
  color: #fff;
}

/* Dashboard Thẻ (Cards) */
.subject-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
  gap: 15px;
  margin-bottom: 30px;
}
.subject-card {
  background: var(--surface);
  border: 1px solid var(--border);
  padding: 20px;
  border-radius: 15px;
  cursor: pointer;
  transition: 0.2s;
  position: relative;
  overflow: hidden;
}
.subject-card:hover {
  background: rgba(59, 130, 246, 0.1);
  border-color: var(--accent);
  transform: translateY(-3px);
}
.subject-card h4 {
  margin: 0 0 10px 0;
  color: var(--accent);
  font-size: 1.2rem;
}
.subject-card p {
  margin: 0;
  font-size: 0.9rem;
  color: var(--muted);
}

.quiz-card {
  background: var(--surface);
  padding: 20px;
  border-radius: 15px;
  margin-bottom: 15px;
  border: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  gap: 15px;
}
@media (min-width: 600px) {
  .quiz-card {
    flex-direction: row;
    justify-content: space-between;
    align-items: center;
  }
}
.quiz-card h4 {
  margin: 0 0 8px 0;
  color: var(--ink);
  font-size: 1.1rem;
}
.quiz-card small {
  color: var(--muted);
  display: flex;
  align-items: center;
  gap: 5px;
  flex-wrap: wrap;
}
.quiz-card .teacher-name {
  font-weight: bold;
  color: var(--accent);
  max-width: 150px;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  display: inline-block;
  vertical-align: bottom;
}
.quiz-card button {
  width: auto;
  margin: 0;
  padding: 10px 20px;
}

/* Giao diện câu hỏi */
.question-box {
  background: var(--surface);
  padding: 20px;
  border-radius: 10px;
  margin-bottom: 20px;
  border: 1px solid var(--border);
}
.option-label {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 12px;
  background: var(--input-bg);
  border-radius: 8px;
  margin-bottom: 10px;
  cursor: pointer;
  border: 1px solid transparent;
  transition: 0.2s;
}
.option-label:hover {
  border-color: var(--accent);
  background: rgba(59, 130, 246, 0.1);
}
.option-label input {
  width: auto;
  margin: 0;
  transform: scale(1.2);
}

.msg-error {
  color: var(--bad);
  margin-bottom: 15px;
  font-weight: bold;
}
.msg-success {
  color: var(--good);
  margin-bottom: 15px;
  font-weight: bold;
}

table {
  width: 100%;
  border-collapse: collapse;
  margin-top: 10px;
}
th,
td {
  padding: 12px;
  text-align: left;
  border-bottom: 1px solid var(--border);
  color: var(--ink);
}
th {
  color: var(--accent);
  font-weight: bold;
}