/**
 * Student Revision & MCQ Practice Design System
 * Mobile-First, Fast, Clean, Premium Educational UI
 */

:root {
  --primary: #2563eb;
  --primary-hover: #1d4ed8;
  --primary-light: #eff6ff;
  --primary-text: #1e40af;
  
  --bg: #f8fafc;
  --surface: #ffffff;
  --surface-subtle: #f1f5f9;
  --surface-card: #ffffff;
  
  --text-main: #0f172a;
  --text-muted: #64748b;
  --text-light: #94a3b8;
  
  --border: #e2e8f0;
  --border-focus: #93c5fd;
  
  --success: #10b981;
  --success-bg: #ecfdf5;
  --success-border: #a7f3d0;
  --success-text: #065f46;
  
  --error: #ef4444;
  --error-bg: #fef2f2;
  --error-border: #fecaca;
  --error-text: #991b1b;
  
  --warning: #f59e0b;
  --warning-bg: #fffbeb;
  --warning-border: #fde68a;
  --warning-text: #92400e;
  
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 14px;
  --radius-full: 9999px;
  
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.07), 0 2px 4px -2px rgba(0, 0, 0, 0.05);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.08), 0 4px 6px -4px rgba(0, 0, 0, 0.04);
  
  --font-sans: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --bottom-nav-height: 64px;
  --header-height: 60px;
}

/* Reset & Box Sizing */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.5;
  color: var(--text-main);
  background-color: var(--bg);
  -webkit-font-smoothing: antialiased;
  -webkit-tap-highlight-color: transparent;
}

body {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  background-color: var(--bg);
  color: var(--text-main);
  overflow-x: hidden;
}

/* Base Elements */
a {
  color: var(--primary);
  text-decoration: none;
  transition: color 0.15s ease;
}
a:hover {
  color: var(--primary-hover);
}

h1, h2, h3, h4, h5, h6 {
  font-weight: 700;
  line-height: 1.25;
  color: var(--text-main);
}

h1 { font-size: 1.625rem; }
h2 { font-size: 1.375rem; }
h3 { font-size: 1.125rem; }
h4 { font-size: 1rem; }

p {
  color: var(--text-muted);
}

/* Layout Containers */
.app-container {
  width: 100%;
  max-width: 960px;
  margin: 0 auto;
  padding: 16px;
  flex: 1;
}

.app-container-narrow {
  max-width: 680px;
}

.practice-container {
  max-width: 640px;
  margin: 0 auto;
  padding: 12px 16px 80px;
}

.student-main-content {
  padding-bottom: calc(var(--bottom-nav-height) + 24px);
}

/* Top App Header */
.app-header {
  height: var(--header-height);
  background-color: var(--surface);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 40;
  display: flex;
  align-items: center;
}

.app-header-inner {
  width: 100%;
  max-width: 960px;
  margin: 0 auto;
  padding: 0 16px;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.brand-logo {
  display: flex;
  align-items: center;
  gap: 10px;
  font-weight: 800;
  font-size: 1.125rem;
  color: var(--text-main);
}

.brand-badge {
  background: var(--primary);
  color: #ffffff;
  padding: 4px 8px;
  border-radius: var(--radius-sm);
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.5px;
}

.header-actions {
  display: flex;
  align-items: center;
  gap: 12px;
}

/* Cards & Surfaces */
.card {
  background-color: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 20px;
  box-shadow: var(--shadow-sm);
  transition: transform 0.15s ease, box-shadow 0.15s ease, border-color 0.15s ease;
}

.card-interactive:hover {
  border-color: var(--primary);
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
}

.card-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 14px;
}

.card-title {
  font-size: 1.125rem;
  font-weight: 700;
  color: var(--text-main);
}

.card-subtitle {
  font-size: 0.875rem;
  color: var(--text-muted);
  margin-top: 2px;
}

/* Modern Grid */
.grid-2 {
  display: grid;
  grid-template-columns: 1fr;
  gap: 16px;
}
@media (min-width: 640px) {
  .grid-2 {
    grid-template-columns: repeat(2, 1fr);
  }
}

.grid-3 {
  display: grid;
  grid-template-columns: 1fr;
  gap: 16px;
}
@media (min-width: 640px) {
  .grid-3 {
    grid-template-columns: repeat(2, 1fr);
  }
}
@media (min-width: 860px) {
  .grid-3 {
    grid-template-columns: repeat(3, 1fr);
  }
}

.grid-4 {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 12px;
}
@media (min-width: 640px) {
  .grid-4 {
    grid-template-columns: repeat(4, 1fr);
    gap: 16px;
  }
}

/* Stat Widgets */
.stat-box {
  background-color: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 16px;
  display: flex;
  flex-direction: column;
}

.stat-value {
  font-size: 1.5rem;
  font-weight: 800;
  color: var(--text-main);
  line-height: 1.2;
}

.stat-label {
  font-size: 0.8125rem;
  color: var(--text-muted);
  font-weight: 600;
  margin-top: 4px;
}

/* Practice UI & MCQ Option Cards */
.practice-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 12px;
}

.back-btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text-muted);
  padding: 6px 10px;
  border-radius: var(--radius-sm);
  background: transparent;
  border: none;
  cursor: pointer;
}
.back-btn:hover {
  background: var(--surface-subtle);
  color: var(--text-main);
}

.progress-wrap {
  width: 100%;
  margin-bottom: 16px;
}

.progress-info {
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 0.8125rem;
  font-weight: 600;
  color: var(--text-muted);
  margin-bottom: 6px;
}

.progress-bar-bg {
  width: 100%;
  height: 8px;
  background-color: var(--border);
  border-radius: var(--radius-full);
  overflow: hidden;
}

.progress-bar-fill {
  height: 100%;
  background-color: var(--primary);
  border-radius: var(--radius-full);
  transition: width 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

/* Question Box */
.question-card {
  background-color: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 22px 20px;
  margin-bottom: 18px;
  box-shadow: var(--shadow-sm);
}

.question-badge {
  display: inline-block;
  font-size: 0.75rem;
  font-weight: 700;
  color: var(--primary-text);
  background: var(--primary-light);
  padding: 3px 8px;
  border-radius: var(--radius-sm);
  margin-bottom: 10px;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.question-text {
  font-size: 1.125rem;
  font-weight: 600;
  line-height: 1.55;
  color: var(--text-main);
}

/* MCQ Options */
.options-list {
  display: flex;
  flex-direction: column;
  gap: 12px;
  margin-bottom: 20px;
}

.option-card {
  position: relative;
  display: flex;
  align-items: center;
  gap: 14px;
  padding: 16px 18px;
  background-color: var(--surface);
  border: 2px solid var(--border);
  border-radius: var(--radius-md);
  cursor: pointer;
  user-select: none;
  transition: all 0.15s ease-in-out;
  text-align: left;
  width: 100%;
  font-family: inherit;
  font-size: 1rem;
  color: var(--text-main);
}

.option-card:hover:not(.disabled) {
  border-color: var(--primary);
  background-color: #fafbfc;
  transform: translateY(-1px);
}

.option-card:active:not(.disabled) {
  transform: translateY(0);
}

.option-letter {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 34px;
  height: 34px;
  border-radius: var(--radius-sm);
  background-color: var(--surface-subtle);
  border: 1px solid var(--border);
  font-weight: 700;
  font-size: 0.9375rem;
  color: var(--text-main);
  flex-shrink: 0;
  transition: all 0.15s ease;
}

.option-text {
  flex: 1;
  font-weight: 500;
  line-height: 1.45;
}

/* Selected state */
.option-card.selected {
  border-color: var(--primary);
  background-color: var(--primary-light);
}
.option-card.selected .option-letter {
  background-color: var(--primary);
  color: #ffffff;
  border-color: var(--primary);
}

/* Correct Answer State */
.option-card.correct {
  border-color: var(--success);
  background-color: var(--success-bg);
}
.option-card.correct .option-letter {
  background-color: var(--success);
  color: #ffffff;
  border-color: var(--success);
}
.option-card.correct::after {
  content: "✓";
  font-weight: 800;
  color: var(--success);
  font-size: 1.25rem;
  margin-left: 8px;
}

/* Incorrect Answer State */
.option-card.incorrect {
  border-color: var(--error);
  background-color: var(--error-bg);
}
.option-card.incorrect .option-letter {
  background-color: var(--error);
  color: #ffffff;
  border-color: var(--error);
}
.option-card.incorrect::after {
  content: "✕";
  font-weight: 800;
  color: var(--error);
  font-size: 1.25rem;
  margin-left: 8px;
}

.option-card.disabled {
  cursor: default;
}

/* Feedback & Explanation Box */
.feedback-box {
  background-color: var(--surface);
  border-radius: var(--radius-lg);
  padding: 18px 20px;
  margin-top: 18px;
  border: 1px solid var(--border);
  box-shadow: var(--shadow-sm);
  animation: fadeIn 0.2s ease;
}

.feedback-banner {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 1.0625rem;
  font-weight: 700;
  margin-bottom: 12px;
}

.feedback-banner.correct {
  color: var(--success);
}

.feedback-banner.incorrect {
  color: var(--error);
}

.explanation-title {
  font-size: 0.8125rem;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  font-weight: 700;
  color: var(--text-muted);
  margin-bottom: 6px;
}

.explanation-body {
  font-size: 0.9375rem;
  line-height: 1.55;
  color: var(--text-main);
  background: var(--surface-subtle);
  padding: 12px 14px;
  border-radius: var(--radius-md);
  margin-bottom: 16px;
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 11px 22px;
  font-size: 0.9375rem;
  font-weight: 600;
  border-radius: var(--radius-md);
  border: 1px solid transparent;
  cursor: pointer;
  transition: all 0.15s ease;
  white-space: nowrap;
  text-decoration: none;
  font-family: inherit;
  min-height: 44px;
}

.btn-primary {
  background-color: var(--primary);
  color: #ffffff;
}
.btn-primary:hover {
  background-color: var(--primary-hover);
  color: #ffffff;
}

.btn-secondary {
  background-color: var(--surface);
  border-color: var(--border);
  color: var(--text-main);
}
.btn-secondary:hover {
  background-color: var(--surface-subtle);
  border-color: var(--text-muted);
}

.btn-outline {
  background-color: transparent;
  border-color: var(--primary);
  color: var(--primary);
}
.btn-outline:hover {
  background-color: var(--primary-light);
}

.btn-block {
  display: flex;
  width: 100%;
}

.btn-sm {
  padding: 6px 12px;
  font-size: 0.8125rem;
  min-height: 32px;
}

.btn-lg {
  padding: 14px 28px;
  font-size: 1.0625rem;
  min-height: 50px;
}

/* Badges */
.badge {
  display: inline-flex;
  align-items: center;
  padding: 3px 8px;
  border-radius: var(--radius-sm);
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.3px;
}

.badge-primary {
  background: var(--primary-light);
  color: var(--primary-text);
}

.badge-success {
  background: var(--success-bg);
  color: var(--success-text);
}

.badge-danger {
  background: var(--error-bg);
  color: var(--error-text);
}

.badge-warning {
  background: var(--warning-bg);
  color: var(--warning-text);
}

/* Alert Boxes */
.alert {
  display: flex;
  align-items: flex-start;
  gap: 12px;
  padding: 12px 16px;
  border-radius: var(--radius-md);
  margin-bottom: 16px;
  font-size: 0.9375rem;
}

.alert-success {
  background-color: var(--success-bg);
  border: 1px solid var(--success-border);
  color: var(--success-text);
}

.alert-error {
  background-color: var(--error-bg);
  border: 1px solid var(--error-border);
  color: var(--error-text);
}

.alert-warning {
  background-color: var(--warning-bg);
  border: 1px solid var(--warning-border);
  color: var(--warning-text);
}

.alert-close {
  background: none;
  border: none;
  font-size: 1.25rem;
  cursor: pointer;
  color: inherit;
  margin-left: auto;
  line-height: 1;
}

/* Forms */
.form-group {
  margin-bottom: 16px;
}

.form-label {
  display: block;
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text-main);
  margin-bottom: 6px;
}

.form-input, .form-select, .form-textarea {
  width: 100%;
  padding: 10px 14px;
  font-size: 0.9375rem;
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  background-color: var(--surface);
  color: var(--text-main);
  font-family: inherit;
  transition: border-color 0.15s ease, box-shadow 0.15s ease;
  min-height: 44px;
}

.form-input:focus, .form-select:focus, .form-textarea:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.15);
}

.form-help {
  font-size: 0.8125rem;
  color: var(--text-muted);
  margin-top: 4px;
}

/* Mobile Bottom Navigation */
.mobile-bottom-nav {
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  height: var(--bottom-nav-height);
  background-color: var(--surface);
  border-top: 1px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: space-around;
  z-index: 50;
  padding-bottom: env(safe-area-inset-bottom);
  box-shadow: 0 -2px 8px rgba(0, 0, 0, 0.04);
}

.bottom-nav-item {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 3px;
  color: var(--text-muted);
  font-size: 0.75rem;
  font-weight: 600;
  padding: 6px 12px;
  text-decoration: none;
  flex: 1;
}

.bottom-nav-item.active {
  color: var(--primary);
}

.bottom-nav-item .icon {
  width: 22px;
  height: 22px;
}

/* Icons */
.icon {
  width: 18px;
  height: 18px;
  display: inline-block;
  vertical-align: middle;
  flex-shrink: 0;
}

.icon-lg {
  width: 24px;
  height: 24px;
}

/* Empty States */
.empty-state {
  text-align: center;
  padding: 48px 20px;
  background-color: var(--surface);
  border: 1px dashed var(--border);
  border-radius: var(--radius-lg);
}

.empty-state-icon {
  width: 48px;
  height: 48px;
  margin: 0 auto 14px;
  color: var(--text-light);
}

.empty-state-title {
  font-size: 1.125rem;
  font-weight: 700;
  color: var(--text-main);
  margin-bottom: 6px;
}

.empty-state-desc {
  font-size: 0.875rem;
  color: var(--text-muted);
  max-width: 360px;
  margin: 0 auto 18px;
}

/* Admin Table */
.table-responsive {
  width: 100%;
  overflow-x: auto;
  border-radius: var(--radius-lg);
  border: 1px solid var(--border);
  background: var(--surface);
}

.table {
  width: 100%;
  border-collapse: collapse;
  text-align: left;
  font-size: 0.875rem;
}

.table th {
  background-color: var(--surface-subtle);
  padding: 12px 16px;
  font-weight: 700;
  color: var(--text-muted);
  border-bottom: 1px solid var(--border);
  text-transform: uppercase;
  font-size: 0.75rem;
  letter-spacing: 0.5px;
}

.table td {
  padding: 14px 16px;
  border-bottom: 1px solid var(--border);
  color: var(--text-main);
}

.table tr:last-child td {
  border-bottom: none;
}

.table tr:hover td {
  background-color: #fafbfc;
}

/* Admin Sidebar & Layout */
.admin-layout {
  display: flex;
  min-height: calc(100vh - var(--header-height));
}

.admin-sidebar {
  width: 240px;
  background-color: var(--surface);
  border-right: 1px solid var(--border);
  padding: 20px 12px;
  display: flex;
  flex-direction: column;
  gap: 6px;
}

@media (max-width: 768px) {
  .admin-sidebar {
    display: none;
  }
}

.admin-nav-item {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 10px 14px;
  border-radius: var(--radius-md);
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text-muted);
  text-decoration: none;
  transition: all 0.15s ease;
}

.admin-nav-item:hover, .admin-nav-item.active {
  background-color: var(--primary-light);
  color: var(--primary-text);
}

.admin-content {
  flex: 1;
  padding: 24px;
  background-color: var(--bg);
  max-width: 1200px;
}

/* Animations */
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(4px); }
  to { opacity: 1; transform: translateY(0); }
}