:root {
  --primary: #6366f1;
  --primary-hover: #4f46e5;
  --bg: #f8fafc;
  --surface: #ffffff;
  --surface-hover: #f1f5f9;
  --text: #0f172a;
  --text-muted: #64748b;
  --accent: #10b981;
  --glass: rgba(0, 0, 0, 0.03);
  --glass-border: rgba(0, 0, 0, 0.1);
  --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  --daily-gradient: linear-gradient(135deg, #6366f1 0%, #a855f7 100%);
}

[data-theme="dark"] {
  --bg: #0f172a;
  --surface: #1e293b;
  --surface-hover: #334155;
  --text: #f8fafc;
  --text-muted: #94a3b8;
  --glass: rgba(255, 255, 255, 0.03);
  --glass-border: rgba(255, 255, 255, 0.1);
  --daily-gradient: linear-gradient(135deg, #4f46e5 0%, #9333ea 100%);
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: 'Inter', system-ui, -apple-system, sans-serif;
}

body {
  background-color: var(--bg);
  color: var(--text);
  min-height: 100vh;
  line-height: 1.6;
  overflow-x: hidden;
}

.container {
  max-width: 1100px;
  margin: 0 auto;
  padding: 2rem;
}

/* Header & Glassmorphism */
header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 1.5rem 0;
  margin-bottom: 4rem;
}

.logo {
  font-size: 1.5rem;
  font-weight: 800;
  background: linear-gradient(135deg, var(--primary), #a855f7);
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
  letter-spacing: -1px;
}

.user-stats {
  display: flex;
  align-items: center;
  gap: 1rem;
  background: var(--glass);
  padding: 0.5rem 1rem;
  border-radius: 12px;
  border: 1px solid var(--glass-border);
  font-weight: 600;
  font-size: 0.9rem;
}

#gpa-display {
  color: var(--primary);
}

#streak-display {
  color: #f97316;
}

.glass-card {
  background: var(--glass);
  backdrop-filter: blur(12px);
  border: 1px solid var(--glass-border);
  border-radius: 24px;
  padding: 2rem;
  transition: var(--transition);
}

.glass-card:hover {
  background: rgba(255, 255, 255, 0.05);
  transform: translateY(-4px);
  border-color: rgba(255, 255, 255, 0.2);
}

/* Typography */
h1 {
  font-size: 3.5rem;
  font-weight: 800;
  margin-bottom: 1.5rem;
  line-height: 1.1;
  letter-spacing: -2px;
}

.tagline {
  color: var(--text-muted);
  font-size: 1.25rem;
  max-width: 600px;
  margin-bottom: 3rem;
}

/* Course Grid */
.course-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  gap: 2rem;
  margin-top: 2rem;
}

.course-card {
  cursor: pointer;
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.course-icon {
  width: 48px;
  height: 48px;
  background: var(--primary);
  border-radius: 12px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.5rem;
  margin-bottom: 0.5rem;
}

.course-card h3 {
  font-size: 1.5rem;
  font-weight: 700;
}

.course-card p {
  color: var(--text-muted);
  font-size: 0.95rem;
  flex-grow: 1;
}

/* Buttons */
.btn {
  padding: 0.75rem 1.5rem;
  border-radius: 12px;
  font-weight: 600;
  border: none;
  cursor: pointer;
  transition: var(--transition);
  text-decoration: none;
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
}

.btn-primary {
  background: var(--primary);
  color: white;
}

.btn-primary:hover {
  background: var(--primary-hover);
  box-shadow: 0 0 20px rgba(99, 102, 241, 0.4);
}

/* Lesson View */
.view {
  display: none;
  animation: fadeIn 0.4s ease-out;
}

.view.active {
  display: block;
}

@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translateY(10px);
  }

  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.lesson-content {
  max-width: 800px;
  margin: 0 auto;
}

.back-btn {
  margin-bottom: 2rem;
  color: var(--text-muted);
}

.back-btn:hover {
  color: var(--text);
}

/* Quiz Styles */
.quiz-options {
  display: flex;
  flex-direction: column;
  gap: 1rem;
  margin: 2rem 0;
}

.option-btn {
  background: var(--surface);
  border: 1px solid var(--glass-border);
  padding: 1rem 1.5rem;
  border-radius: 12px;
  color: var(--text);
  text-align: left;
  cursor: pointer;
  transition: var(--transition);
}

.option-btn:hover {
  background: var(--surface-hover);
}

.option-btn.correct {
  background: rgba(16, 185, 129, 0.2);
  border-color: var(--accent);
}

.option-btn.incorrect {
  background: rgba(239, 68, 68, 0.2);
  border-color: #ef4444;
}

/* Progress bar */
.progress-container {
  width: 100%;
  height: 6px;
  background: var(--surface);
  border-radius: 3px;
  margin: 2rem 0;
  overflow: hidden;
}

.progress-bar {
  height: 100%;
  background: var(--primary);
  width: 0%;
  transition: width 0.5s ease;
}

/* Dark Mode Toggle */
#theme-toggle {
  background: var(--surface);
  border: 1px solid var(--glass-border);
  color: var(--text);
  width: 40px;
  height: 40px;
  border-radius: 10px;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  font-size: 1.2rem;
  transition: var(--transition);
}

#theme-toggle:hover {
  background: var(--surface-hover);
  transform: scale(1.05);
}

/* Completion Badge */
.completion-badge {
  position: absolute;
  top: 1.5rem;
  right: 1.5rem;
  background: var(--accent);
  color: white;
  padding: 4px 10px;
  border-radius: 20px;
  font-size: 0.7rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  box-shadow: 0 4px 12px rgba(16, 185, 129, 0.3);
}

.course-card.completed {
  border: 1px solid var(--accent);
}

.course-card {
  position: relative;
}

/* Achievement Section */
#achievements-section {
  margin-top: 4rem;
  padding-top: 2rem;
  border-top: 1px solid var(--glass-border);
}

.achievement-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 1.5rem;
  margin-top: 1.5rem;
}

.achievement-card {
  padding: 1.5rem;
  text-align: center;
  opacity: 0.5;
  filter: grayscale(1);
  transition: var(--transition);
}

.achievement-card.unlocked {
  opacity: 1;
  filter: grayscale(0);
}

.achievement-icon {
  font-size: 2rem;
  margin-bottom: 0.5rem;
}

.achievement-card h4 {
  font-size: 1rem;
  margin-bottom: 0.25rem;
}

.achievement-card p {
  font-size: 0.8rem;
  color: var(--text-muted);
}

/* Daily Challenge Card */
.daily-card {
  margin: 2rem 0;
  position: relative;
  overflow: hidden;
  border: 1px solid var(--glass-border);
  background: var(--surface);
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
  box-shadow: 0 10px 30px -10px rgba(99, 102, 241, 0.2);
}

[data-theme="dark"] .daily-card {
  background: var(--surface);
  box-shadow: 0 10px 30px -10px rgba(0, 0, 0, 0.5);
}

.daily-badge {
  position: absolute;
  top: 0;
  left: 0;
  background: var(--daily-gradient);
  color: white;
  padding: 4px 12px;
  border-radius: 0 0 12px 0;
  font-size: 0.7rem;
  font-weight: 800;
  letter-spacing: 1px;
}

.daily-content {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 2rem;
}

.daily-info h3 {
  font-size: 1.5rem;
  margin-bottom: 0.5rem;
}

.daily-card.completed {
  opacity: 0.8;
  border-color: var(--accent);
  background-image: linear-gradient(var(--surface), var(--surface)), var(--accent);
}

@media (max-width: 640px) {
  .daily-content {
    flex-direction: column;
    align-items: flex-start;
  }

  .btn-primary {
    width: 100%;
    justify-content: center;
  }
}