/* ==============================================
   CSS Custom Properties (Dark Theme)
   ============================================== */
:root {
  /* Colors - Dark Theme */
  --color-primary: #6366f1;
  --color-primary-dark: #4f46e5;
  --color-primary-light: #818cf8;
  --color-secondary: #10b981;
  --color-secondary-dark: #059669;
  --color-danger: #ef4444;
  --color-danger-dark: #dc2626;
  --color-warning: #f59e0b;
  
  /* Background Colors */
  --color-bg-primary: #0f0f23;
  --color-bg-secondary: #1a1a2e;
  --color-bg-tertiary: #16213e;
  --color-bg-card: #1e1e3f;
  --color-bg-modal: rgba(15, 15, 35, 0.95);
  
  /* Text Colors */
  --color-text-primary: #f8fafc;
  --color-text-secondary: #cbd5e1;
  --color-text-muted: #94a3b8;
  --color-text-inverse: #1e293b;
  
  /* Border Colors */
  --color-border: #334155;
  --color-border-light: #475569;
  --color-border-focus: var(--color-primary);
  
  /* Shadows */
  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.3);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.4), 0 2px 4px -1px rgba(0, 0, 0, 0.3);
  --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.5), 0 4px 6px -2px rgba(0, 0, 0, 0.3);
  --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.6), 0 10px 10px -5px rgba(0, 0, 0, 0.3);
  
  /* Typography */
  --font-family-base: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
  --font-size-xs: 0.75rem;
  --font-size-sm: 0.875rem;
  --font-size-base: 1rem;
  --font-size-lg: 1.125rem;
  --font-size-xl: 1.25rem;
  --font-size-2xl: 1.5rem;
  --font-size-3xl: 1.875rem;
  
  --font-weight-normal: 400;
  --font-weight-medium: 500;
  --font-weight-semibold: 600;
  --font-weight-bold: 700;
  
  --line-height-tight: 1.25;
  --line-height-normal: 1.5;
  --line-height-relaxed: 1.625;
  
  /* Spacing */
  --spacing-xs: 0.25rem;
  --spacing-sm: 0.5rem;
  --spacing-md: 1rem;
  --spacing-lg: 1.5rem;
  --spacing-xl: 2rem;
  --spacing-2xl: 3rem;
  
  /* Borders */
  --border-radius-sm: 0.375rem;
  --border-radius-md: 0.5rem;
  --border-radius-lg: 0.75rem;
  --border-radius-xl: 1rem;
  --border-radius-full: 9999px;
  
  /* Animation */
  --transition-fast: 150ms ease-in-out;
  --transition-normal: 300ms ease-in-out;
  --transition-slow: 500ms ease-in-out;
  
  /* Touch Targets */
  --touch-target-min: 44px;
  
  /* Z-index */
  --z-modal: 1000;
  --z-toast: 1100;
  --z-fab: 100;
}

/* ==============================================
   Base Styles & Reset
   ============================================== */
*, *::before, *::after {
  box-sizing: border-box;
}

html {
  font-size: 16px;
  -webkit-text-size-adjust: 100%;
  -webkit-tap-highlight-color: transparent;
}

body {
  margin: 0;
  padding: 0;
  font-family: var(--font-family-base);
  font-size: var(--font-size-base);
  font-weight: var(--font-weight-normal);
  line-height: var(--line-height-normal);
  color: var(--color-text-primary);
  background-color: var(--color-bg-primary);
  min-height: 100vh;
  overflow-x: hidden;
}

/* ==============================================
   Typography
   ============================================== */
h1, h2, h3, h4, h5, h6 {
  margin: 0 0 var(--spacing-md) 0;
  font-weight: var(--font-weight-semibold);
  line-height: var(--line-height-tight);
  color: var(--color-text-primary);
}

h1 { font-size: var(--font-size-3xl); }
h2 { font-size: var(--font-size-2xl); }
h3 { font-size: var(--font-size-xl); }

p {
  margin: 0 0 var(--spacing-md) 0;
  color: var(--color-text-secondary);
}

/* ==============================================
   Header
   ============================================== */
.header {
  position: sticky;
  top: 0;
  z-index: 50;
  background: var(--color-bg-secondary);
  border-bottom: 1px solid var(--color-border);
  box-shadow: var(--shadow-sm);
  backdrop-filter: blur(8px);
}

.header-content {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--spacing-md) var(--spacing-lg);
  max-width: 1200px;
  margin: 0 auto;
}

.app-title {
  font-size: var(--font-size-2xl);
  font-weight: var(--font-weight-bold);
  color: var(--color-text-primary);
  margin: 0;
}

.add-workout-btn {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
  padding: var(--spacing-sm) var(--spacing-lg);
  min-height: var(--touch-target-min);
  background: var(--color-primary);
  color: white;
  border: none;
  border-radius: var(--border-radius-full);
  font-size: var(--font-size-sm);
  font-weight: var(--font-weight-medium);
  cursor: pointer;
  transition: all var(--transition-fast);
  box-shadow: var(--shadow-md);
}

.add-workout-btn:hover,
.add-workout-btn:focus {
  background: var(--color-primary-dark);
  transform: translateY(-1px);
  box-shadow: var(--shadow-lg);
  outline: none;
}

.add-workout-btn:active {
  transform: translateY(0);
  box-shadow: var(--shadow-md);
}

.plus-icon {
  font-size: var(--font-size-lg);
  font-weight: var(--font-weight-bold);
}

/* ==============================================
   Main Content
   ============================================== */
.main-content {
  max-width: 1200px;
  margin: 0 auto;
  padding: var(--spacing-lg);
  min-height: calc(100vh - 80px);
}

/* ==============================================
   Exercises Section
   ============================================== */
.exercises-section {
  margin-bottom: var(--spacing-2xl);
}

.section-header {
  margin-bottom: var(--spacing-xl);
}

.section-header h2 {
  margin-bottom: var(--spacing-lg);
  color: var(--color-text-primary);
}

.filter-tabs {
  display: flex;
  gap: var(--spacing-sm);
  overflow-x: auto;
  padding-bottom: var(--spacing-xs);
  scrollbar-width: none;
  -ms-overflow-style: none;
}

.filter-tabs::-webkit-scrollbar {
  display: none;
}

.filter-tab {
  flex-shrink: 0;
  padding: var(--spacing-sm) var(--spacing-lg);
  min-height: var(--touch-target-min);
  background: var(--color-bg-card);
  color: var(--color-text-secondary);
  border: 1px solid var(--color-border);
  border-radius: var(--border-radius-full);
  font-size: var(--font-size-sm);
  font-weight: var(--font-weight-medium);
  cursor: pointer;
  transition: all var(--transition-fast);
}

.filter-tab:hover,
.filter-tab:focus {
  background: var(--color-bg-tertiary);
  color: var(--color-text-primary);
  outline: none;
}

.filter-tab.active {
  background: var(--color-primary);
  color: white;
  border-color: var(--color-primary);
}

/* ==============================================
   Exercises Grid
   ============================================== */
.exercises-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--spacing-lg);
}

@media (min-width: 640px) {
  .exercises-grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (min-width: 1024px) {
  .exercises-grid {
    grid-template-columns: repeat(3, 1fr);
  }
}

.exercise-card {
  background: var(--color-bg-card);
  border: 1px solid var(--color-border);
  border-radius: var(--border-radius-lg);
  padding: var(--spacing-lg);
  cursor: pointer;
  transition: all var(--transition-fast);
  position: relative;
  overflow: hidden;
}

.exercise-card:hover,
.exercise-card:focus {
  background: var(--color-bg-tertiary);
  border-color: var(--color-border-light);
  transform: translateY(-2px);
  box-shadow: var(--shadow-lg);
  outline: none;
}

.exercise-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: var(--color-primary);
  transform: scaleX(0);
  transition: transform var(--transition-fast);
}

.exercise-card:hover::before,
.exercise-card:focus::before {
  transform: scaleX(1);
}

.exercise-name {
  font-size: var(--font-size-lg);
  font-weight: var(--font-weight-semibold);
  color: var(--color-text-primary);
  margin-bottom: var(--spacing-sm);
}

.exercise-category {
  display: inline-block;
  padding: var(--spacing-xs) var(--spacing-sm);
  background: var(--color-bg-secondary);
  color: var(--color-text-muted);
  font-size: var(--font-size-xs);
  font-weight: var(--font-weight-medium);
  border-radius: var(--border-radius-sm);
  text-transform: uppercase;
  letter-spacing: 0.5px;
  margin-bottom: var(--spacing-md);
}

.last-workout {
  font-size: var(--font-size-sm);
  color: var(--color-text-secondary);
}

.last-workout-stats {
  display: flex;
  gap: var(--spacing-md);
  margin-top: var(--spacing-sm);
}

.stat {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-xs);
}

.stat-label {
  font-size: var(--font-size-xs);
  color: var(--color-text-muted);
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.stat-value {
  font-size: var(--font-size-lg);
  font-weight: var(--font-weight-semibold);
  color: var(--color-primary-light);
}

/* ==============================================
   Loading Spinner
   ============================================== */
.loading-spinner {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: var(--spacing-2xl);
  color: var(--color-text-muted);
}

.spinner {
  width: 40px;
  height: 40px;
  border: 3px solid var(--color-border);
  border-top: 3px solid var(--color-primary);
  border-radius: 50%;
  animation: spin 1s linear infinite;
  margin-bottom: var(--spacing-md);
}

@keyframes spin {
  0% { transform: rotate(0deg); }
  100% { transform: rotate(360deg); }
}

/* ==============================================
   Recent Workouts Section
   ============================================== */
.recent-workouts-section h2 {
  margin-bottom: var(--spacing-lg);
  color: var(--color-text-primary);
}

.recent-workouts-list {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-md);
}

.workout-item {
  background: var(--color-bg-card);
  border: 1px solid var(--color-border);
  border-radius: var(--border-radius-md);
  padding: var(--spacing-lg);
  transition: all var(--transition-fast);
}

.workout-item:hover {
  background: var(--color-bg-tertiary);
  border-color: var(--color-border-light);
}

.workout-header {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  margin-bottom: var(--spacing-sm);
}

.workout-exercise {
  font-size: var(--font-size-lg);
  font-weight: var(--font-weight-semibold);
  color: var(--color-text-primary);
}

.workout-date {
  font-size: var(--font-size-sm);
  color: var(--color-text-muted);
}

.workout-stats {
  display: flex;
  gap: var(--spacing-lg);
}

/* ==============================================
   Modal Styles
   ============================================== */
.modal {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  z-index: var(--z-modal);
  display: flex;
  align-items: center;
  justify-content: center;
  padding: var(--spacing-lg);
  opacity: 0;
  visibility: hidden;
  transition: all var(--transition-normal);
}

.modal.active {
  opacity: 1;
  visibility: visible;
}

.modal-backdrop {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: var(--color-bg-modal);
  backdrop-filter: blur(4px);
}

.modal-content {
  position: relative;
  background: var(--color-bg-card);
  border: 1px solid var(--color-border);
  border-radius: var(--border-radius-xl);
  width: 100%;
  max-width: 500px;
  max-height: 90vh;
  overflow-y: auto;
  box-shadow: var(--shadow-xl);
  transform: scale(0.95) translateY(20px);
  transition: all var(--transition-normal);
}

.modal.active .modal-content {
  transform: scale(1) translateY(0);
}

.modal-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--spacing-xl) var(--spacing-xl) var(--spacing-lg);
  border-bottom: 1px solid var(--color-border);
}

.modal-header h3 {
  margin: 0;
  color: var(--color-text-primary);
}

.modal-close {
  display: flex;
  align-items: center;
  justify-content: center;
  width: var(--touch-target-min);
  height: var(--touch-target-min);
  background: none;
  border: none;
  color: var(--color-text-muted);
  font-size: var(--font-size-2xl);
  cursor: pointer;
  border-radius: var(--border-radius-md);
  transition: all var(--transition-fast);
}

.modal-close:hover,
.modal-close:focus {
  background: var(--color-bg-secondary);
  color: var(--color-text-primary);
  outline: none;
}

/* ==============================================
   Form Styles
   ============================================== */
.workout-form {
  padding: var(--spacing-xl);
}

.form-group {
  margin-bottom: var(--spacing-lg);
}

.form-row {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
  gap: var(--spacing-md);
}

.form-group label {
  display: block;
  margin-bottom: var(--spacing-sm);
  font-size: var(--font-size-sm);
  font-weight: var(--font-weight-medium);
  color: var(--color-text-primary);
}

.form-group input,
.form-group select {
  width: 100%;
  min-height: var(--touch-target-min);
  padding: var(--spacing-sm) var(--spacing-md);
  background: var(--color-bg-secondary);
  color: var(--color-text-primary);
  border: 1px solid var(--color-border);
  border-radius: var(--border-radius-md);
  font-size: var(--font-size-base);
  transition: all var(--transition-fast);
}

.form-group input:focus,
.form-group select:focus {
  outline: none;
  border-color: var(--color-border-focus);
  box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.1);
}

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

.form-actions {
  display: flex;
  gap: var(--spacing-md);
  margin-top: var(--spacing-xl);
  padding-top: var(--spacing-lg);
  border-top: 1px solid var(--color-border);
}

/* ==============================================
   Button Styles
   ============================================== */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--spacing-sm);
  min-height: var(--touch-target-min);
  padding: var(--spacing-sm) var(--spacing-lg);
  font-size: var(--font-size-sm);
  font-weight: var(--font-weight-medium);
  border: 1px solid transparent;
  border-radius: var(--border-radius-md);
  cursor: pointer;
  transition: all var(--transition-fast);
  text-decoration: none;
  flex: 1;
}

.btn:focus {
  outline: none;
  box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.1);
}

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

.btn-primary:hover,
.btn-primary:focus {
  background: var(--color-primary-dark);
  border-color: var(--color-primary-dark);
}

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

.btn-secondary:hover,
.btn-secondary:focus {
  background: var(--color-bg-tertiary);
  border-color: var(--color-border-light);
}

/* ==============================================
   Toast Notifications
   ============================================== */
.toast-container {
  position: fixed;
  top: var(--spacing-lg);
  right: var(--spacing-lg);
  z-index: var(--z-toast);
  display: flex;
  flex-direction: column;
  gap: var(--spacing-sm);
  max-width: 400px;
}

.toast {
  background: var(--color-bg-card);
  color: var(--color-text-primary);
  border: 1px solid var(--color-border);
  border-radius: var(--border-radius-md);
  padding: var(--spacing-lg);
  box-shadow: var(--shadow-lg);
  transform: translateX(100%);
  transition: all var(--transition-normal);
}

.toast.show {
  transform: translateX(0);
}

.toast.success {
  border-left: 4px solid var(--color-secondary);
}

.toast.error {
  border-left: 4px solid var(--color-danger);
}

.toast.warning {
  border-left: 4px solid var(--color-warning);
}

/* ==============================================
   Responsive Design
   ============================================== */
@media (max-width: 640px) {
  .header-content {
    padding: var(--spacing-md);
  }
  
  .app-title {
    font-size: var(--font-size-xl);
  }
  
  .main-content {
    padding: var(--spacing-md);
  }
  
  .modal {
    padding: var(--spacing-md);
  }
  
  .form-row {
    grid-template-columns: 1fr;
  }
  
  .form-actions {
    flex-direction: column;
  }
  
  .toast-container {
    top: var(--spacing-md);
    right: var(--spacing-md);
    left: var(--spacing-md);
    max-width: none;
  }
}

/* ==============================================
   Accessibility
   ============================================== */
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
}

/* Focus visible for keyboard navigation */
.btn:focus-visible,
.exercise-card:focus-visible,
.filter-tab:focus-visible,
input:focus-visible,
select:focus-visible {
  outline: 2px solid var(--color-primary);
  outline-offset: 2px;
}

/* High contrast mode support */
@media (prefers-contrast: high) {
  :root {
    --color-border: #64748b;
    --color-border-light: #94a3b8;
  }
}