/* Reset and base styles */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

:root {
  --bg-primary: #f8fafc;
  --bg-secondary: #ffffff;
  --text-primary: #1e293b;
  --text-secondary: #64748b;
  --border-color: #e2e8f0;
  --accent-color: #3b82f6;
  --accent-hover: #2563eb;
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.1);
  --shadow-md: 0 4px 6px -1px rgba(0,0,0,0.1);
  --card-bg: #ffffff;
  --input-bg: #ffffff;
}

[data-theme="dark"] {
  --bg-primary: #0f172a;
  --bg-secondary: #1e293b;
  --text-primary: #f1f5f9;
  --text-secondary: #94a3b8;
  --border-color: #334155;
  --accent-color: #3b82f6;
  --accent-hover: #60a5fa;
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.3);
  --shadow-md: 0 4px 6px -1px rgba(0,0,0,0.3);
  --card-bg: #1e293b;
  --input-bg: #334155;
}

body {
  font-family: 'Inter', sans-serif;
  background-color: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.5;
  transition: background-color 0.3s, color 0.3s;
  min-height: 100vh;
}

.app {
  max-width: 1400px;
  margin: 0 auto;
  padding: 2rem;
}

/* Header styles */
.header {
  margin-bottom: 2rem;
}

.header-top {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 1.5rem;
}

.logo {
  font-size: 1.5rem;
  font-weight: 600;
  color: var(--text-primary);
}

.header-actions {
  display: flex;
  gap: 1rem;
  align-items: center;
}

.icon-btn {
  background: none;
  border: none;
  font-size: 1.25rem;
  cursor: pointer;
  padding: 0.5rem;
  border-radius: 0.5rem;
  color: var(--text-primary);
  transition: background-color 0.2s;
}

.icon-btn:hover {
  background-color: var(--border-color);
}

/* Button styles */
.btn {
  padding: 0.625rem 1.25rem;
  border-radius: 0.5rem;
  font-weight: 500;
  font-size: 0.875rem;
  cursor: pointer;
  transition: all 0.2s;
  border: 1px solid transparent;
}

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

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

.btn-secondary {
  background-color: var(--bg-secondary);
  color: var(--text-primary);
  border-color: var(--border-color);
}

.btn-secondary:hover {
  background-color: var(--border-color);
}

/* Form styles */
.add-card-form {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr auto;
  gap: 1rem;
  background-color: var(--bg-secondary);
  padding: 1.5rem;
  border-radius: 1rem;
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--border-color);
}

.form-input {
  padding: 0.625rem 1rem;
  border-radius: 0.5rem;
  border: 1px solid var(--border-color);
  background-color: var(--input-bg);
  color: var(--text-primary);
  font-size: 0.875rem;
  transition: border-color 0.2s, box-shadow 0.2s;
}

.form-input:focus {
  outline: none;
  border-color: var(--accent-color);
  box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.1);
}

.form-input::placeholder {
  color: var(--text-secondary);
}

/* Stats bar */
.stats-bar {
  margin-bottom: 1.5rem;
  padding: 0.75rem 1rem;
  background-color: var(--bg-secondary);
  border-radius: 0.5rem;
  border: 1px solid var(--border-color);
  font-size: 0.875rem;
  color: var(--text-secondary);
}

/* Flashcard grid */
.flashcard-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 1.5rem;
}

/* Flashcard styles */
.flashcard {
  aspect-ratio: 3/2;
  cursor: pointer;
  perspective: 1000px;
  transition: transform 0.2s;
}

.flashcard:hover {
  transform: translateY(-2px);
}

.flashcard-inner {
  position: relative;
  width: 100%;
  height: 100%;
  text-align: center;
  transition: transform 0.6s;
  transform-style: preserve-3d;
  border-radius: 1rem;
  box-shadow: var(--shadow-md);
}

.flashcard.flipped .flashcard-inner {
  transform: rotateY(180deg);
}

.card-front, .card-back {
  position: absolute;
  width: 100%;
  height: 100%;
  backface-visibility: hidden;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  padding: 1.5rem;
  border-radius: 1rem;
  background-color: var(--card-bg);
  border: 1px solid var(--border-color);
  overflow: hidden;
}

.card-front {
  background-color: var(--card-bg);
}

.card-back {
  background-color: var(--card-bg);
  transform: rotateY(180deg);
}

.card-category {
  position: absolute;
  top: 0.75rem;
  left: 0.75rem;
  font-size: 0.75rem;
  padding: 0.25rem 0.5rem;
  background-color: var(--accent-color);
  color: white;
  border-radius: 1rem;
  opacity: 0.9;
}

.card-term {
  font-size: 1.25rem;
  font-weight: 600;
  margin-bottom: 0.5rem;
  color: var(--text-primary);
}

.card-definition {
  font-size: 1rem;
  color: var(--text-secondary);
  line-height: 1.5;
}

.delete-btn {
  position: absolute;
  top: 0.75rem;
  right: 0.75rem;
  width: 2rem;
  height: 2rem;
  border-radius: 0.5rem;
  border: none;
  background-color: rgba(239, 68, 68, 0.1);
  color: #ef4444;
  font-size: 1.25rem;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all 0.2s;
  z-index: 10;
}

.delete-btn:hover {
  background-color: #ef4444;
  color: white;
}

/* Empty state */
.empty-state {
  grid-column: 1 / -1;
  text-align: center;
  padding: 4rem 2rem;
  background-color: var(--bg-secondary);
  border-radius: 1rem;
  border: 2px dashed var(--border-color);
  color: var(--text-secondary);
}

.empty-state p {
  margin-bottom: 1rem;
  font-size: 1.125rem;
}

/* Responsive design */
@media (max-width: 768px) {
  .app {
    padding: 1rem;
  }
  
  .add-card-form {
    grid-template-columns: 1fr;
  }
  
  .header-top {
    flex-direction: column;
    gap: 1rem;
    align-items: start;
  }
  
  .flashcard-grid {
    grid-template-columns: 1fr;
  }
}

/* Loading animation */
@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translateY(10px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.flashcard {
  animation: fadeIn 0.3s ease-out;
}