/* ========================================
   SCIENTIFICALLY OPTIMAL UI/UX DESIGN
   Based on research in cognitive psychology,
   accessibility standards, and user experience
   ======================================== */

/* CSS Custom Properties for Design System (maintainability principle) */
:root {
  /* Typography Scale - 1.25 ratio (Major Third) for optimal hierarchy */
  --font-size-xs: 0.64rem;
  --font-size-sm: 0.8rem;
  --font-size-base: 1rem;
  --font-size-lg: 1.25rem;
  --font-size-xl: 1.563rem;
  --font-size-2xl: 1.953rem;
  --font-size-3xl: 2.441rem;

  /* 8px Grid System - improves visual consistency */
  --spacing-xs: 4px;
  --spacing-sm: 8px;
  --spacing-md: 16px;
  --spacing-lg: 24px;
  --spacing-xl: 32px;
  --spacing-2xl: 48px;
  --spacing-3xl: 64px;

  /* Color Psychology & WCAG AA Compliance (4.5:1 contrast) */
  --color-primary: #0066cc; /* Blue: trust, reliability */
  --color-primary-dark: #0052a3;
  --color-success: #16a34a; /* Green: positive actions */
  --color-warning: #f59e0b; /* Amber: caution */
  --color-danger: #dc2626; /* Red: errors, danger */
  
  /* Neutral colors with proper contrast ratios */
  --color-bg-light: #ffffff;
  --color-bg-dark: #0f0f0f;
  --color-text-light: #171717;
  --color-text-dark: #f5f5f5;
  --color-border: #e5e5e5;
  --color-border-dark: #262626;
  
  /* Shadows for depth perception (Material Design principles) */
  --shadow-sm: 0 1px 3px rgba(0, 0, 0, 0.12);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.15);
  --shadow-lg: 0 10px 25px rgba(0, 0, 0, 0.19);
  
  /* Border radius for friendly perception */
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;
  --radius-full: 9999px;
}

/* Base styles following web standards */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box; /* Predictable sizing model */
}

body {
  /* Inter font: designed for UI, optimal readability */
  font-family: 'Inter', 'Segoe UI', 'Helvetica Neue', Arial, sans-serif;
  font-size: var(--font-size-base);
  line-height: 1.6; /* Optimal readability ratio */
  color: var(--color-text-light);
  background-color: var(--color-bg-light);
  transition: all 0.3s ease; /* Smooth theme transitions */
  
  /* Improve text rendering */
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-rendering: optimizeLegibility;
}

/* Skip link for accessibility (WCAG 2.1 AA) */
.skip-link {
  position: absolute;
  top: -40px;
  left: 6px;
  background: var(--color-primary);
  color: white;
  padding: 8px;
  text-decoration: none;
  border-radius: var(--radius-sm);
  z-index: 1000;
}

.skip-link:focus {
  top: 6px; /* Becomes visible when focused */
}

/* Header with semantic structure */
header {
  background: var(--color-bg-light);
  border-bottom: 1px solid var(--color-border);
  box-shadow: var(--shadow-sm);
  position: sticky; /* Keeps navigation accessible */
  top: 0;
  z-index: 100;
}

.nav-container {
  max-width: 1200px; /* Optimal line length principle */
  margin: 0 auto;
  padding: var(--spacing-md) var(--spacing-lg);
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap; /* Responsive flexibility */
}

/* Logo design following hierarchy principles */
.logo {
  font-size: var(--font-size-xl);
  font-weight: 700;
  color: var(--color-primary);
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
  margin: 0;
}

.logo-icon {
  font-size: var(--font-size-2xl);
}

/* Navigation buttons following Fitts's Law */
.nav-buttons {
  display: flex;
  gap: var(--spacing-sm);
  align-items: center;
}

.nav-btn {
  /* Minimum 44px touch target (accessibility guideline) */
  min-height: 44px;
  min-width: 44px;
  padding: var(--spacing-sm) var(--spacing-md);
  border: none;
  border-radius: var(--radius-md);
  background: transparent;
  color: var(--color-text-light);
  cursor: pointer;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 2px;
  
  /* Micro-interactions for user feedback */
  transition: all 0.2s ease;
  position: relative;
}

.nav-btn:hover {
  background: rgba(0, 102, 204, 0.1); /* Subtle feedback */
  transform: translateY(-1px); /* Perceived responsiveness */
}

.nav-btn:active {
  transform: translateY(0); /* Tactile feedback */
}

/* Active state for system status visibility */
.nav-btn.active {
  background: var(--color-primary);
  color: white;
  box-shadow: var(--shadow-sm);
}

.nav-icon {
  font-size: var(--font-size-lg);
}

.nav-text {
  font-size: var(--font-size-xs);
  font-weight: 500;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

/* Theme toggle with clear affordances */
.theme-toggle {
  min-height: 44px;
  min-width: 44px;
  padding: var(--spacing-sm);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-full);
  background: var(--color-bg-light);
  cursor: pointer;
  transition: all 0.2s ease;
  margin-left: var(--spacing-md);
}

.theme-toggle:hover {
  border-color: var(--color-primary);
  box-shadow: var(--shadow-sm);
}

/* Main content area with proper spacing */
main {
  min-height: calc(100vh - 80px); /* Full viewport usage */
  max-width: 1200px;
  margin: 0 auto;
  padding: var(--spacing-lg);
}

.content-wrapper {
  background: var(--color-bg-light);
  border-radius: var(--radius-lg);
  padding: var(--spacing-xl);
  box-shadow: var(--shadow-sm);
  min-height: 400px;
}

/* Image styling following design principles */
.uploaded-image {
  width: 100%;
  max-width: 600px;
  height: auto;
  aspect-ratio: 1 / 1; /* Consistent proportions */
  object-fit: cover;
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-md);
  margin: var(--spacing-md) 0;
  transition: transform 0.2s ease;
}

.uploaded-image:hover {
  transform: scale(1.02); /* Subtle zoom on hover */
}

/* Button styles following Material Design principles */
.btn {
  min-height: 44px; /* Fitts's Law compliance */
  padding: var(--spacing-sm) var(--spacing-lg);
  border: none;
  border-radius: var(--radius-md);
  font-size: var(--font-size-base);
  font-weight: 500;
  cursor: pointer;
  transition: all 0.2s ease;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--spacing-xs);
  text-decoration: none;
}

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

.btn-primary:hover {
  background: var(--color-primary-dark);
  box-shadow: var(--shadow-md);
  transform: translateY(-1px);
}

.btn-secondary {
  background: transparent;
  color: var(--color-primary);
  border: 1px solid var(--color-primary);
}

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

/* Form inputs with good UX practices */
.form-input {
  width: 100%;
  min-height: 44px;
  padding: var(--spacing-sm) var(--spacing-md);
  border: 2px solid var(--color-border);
  border-radius: var(--radius-md);
  font-size: var(--font-size-base);
  transition: border-color 0.2s ease;
  background: var(--color-bg-light);
}

.form-input:focus {
  outline: none;
  border-color: var(--color-primary);
  box-shadow: 0 0 0 3px rgba(0, 102, 204, 0.1);
}

/* UX Info Panel - Educational overlay */
.ux-info-panel {
  position: fixed;
  top: 50%;
  right: var(--spacing-lg);
  transform: translateY(-50%);
  z-index: 1000;
  max-width: 300px;
}

.ux-toggle {
  background: var(--color-primary);
  color: white;
  border: none;
  padding: var(--spacing-sm) var(--spacing-md);
  border-radius: var(--radius-md);
  cursor: pointer;
  font-size: var(--font-size-sm);
  box-shadow: var(--shadow-lg);
  transition: all 0.2s ease;
}

.ux-toggle:hover {
  background: var(--color-primary-dark);
  transform: translateY(-2px);
}

.ux-content {
  background: white;
  border-radius: var(--radius-lg);
  padding: var(--spacing-lg);
  box-shadow: var(--shadow-lg);
  border: 1px solid var(--color-border);
  margin-top: var(--spacing-sm);
  display: none;
  max-height: 400px;
  overflow-y: auto;
}

.ux-content.show {
  display: block;
}

.ux-principle {
  margin-bottom: var(--spacing-md);
  padding: var(--spacing-md);
  background: rgba(0, 102, 204, 0.05);
  border-radius: var(--radius-sm);
  border-left: 3px solid var(--color-primary);
}

.ux-principle h4 {
  color: var(--color-primary);
  font-size: var(--font-size-sm);
  margin-bottom: var(--spacing-xs);
  font-weight: 600;
}

.ux-principle p {
  font-size: var(--font-size-xs);
  line-height: 1.4;
  color: #666;
}

/* Loading states for user feedback */
.loading-overlay {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: rgba(255, 255, 255, 0.9);
  display: none;
  justify-content: center;
  align-items: center;
  flex-direction: column;
  z-index: 2000;
}

.loading-overlay.show {
  display: flex;
}

.loading-spinner {
  width: 32px;
  height: 32px;
  border: 3px solid var(--color-border);
  border-top: 3px solid var(--color-primary);
  border-radius: 50%;
  animation: spin 1s linear infinite;
}

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

/* Toast notifications - better than alert() */
.toast-container {
  position: fixed;
  top: var(--spacing-lg);
  right: var(--spacing-lg);
  z-index: 1500;
  max-width: 400px;
}

.toast {
  background: white;
  border-radius: var(--radius-md);
  padding: var(--spacing-md) var(--spacing-lg);
  margin-bottom: var(--spacing-sm);
  box-shadow: var(--shadow-lg);
  border: 1px solid var(--color-border);
  transform: translateX(100%);
  opacity: 0;
  animation: slideIn 0.3s ease forwards;
}

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

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

@keyframes slideIn {
  to {
    transform: translateX(0);
    opacity: 1;
  }
}

/* Dark mode using CSS custom properties */
.dark-mode {
  background-color: var(--color-bg-dark);
  color: var(--color-text-dark);
}

.dark-mode header {
  background: var(--color-bg-dark);
  border-bottom-color: var(--color-border-dark);
}

.dark-mode .nav-btn {
  color: var(--color-text-dark);
}

.dark-mode .nav-btn:hover {
  background: rgba(255, 255, 255, 0.1);
}

.dark-mode .theme-toggle {
  background: var(--color-bg-dark);
  border-color: var(--color-border-dark);
  color: var(--color-text-dark);
}

.dark-mode .content-wrapper {
  background: var(--color-bg-dark);
  border: 1px solid var(--color-border-dark);
}

.dark-mode .form-input {
  background: var(--color-bg-dark);
  border-color: var(--color-border-dark);
  color: var(--color-text-dark);
}

.dark-mode .ux-content {
  background: var(--color-bg-dark);
  border-color: var(--color-border-dark);
  color: var(--color-text-dark);
}

.dark-mode .toast {
  background: var(--color-bg-dark);
  border-color: var(--color-border-dark);
  color: var(--color-text-dark);
}

/* Responsive design following mobile-first approach */
@media (max-width: 768px) {
  .nav-container {
    padding: var(--spacing-sm) var(--spacing-md);
  }
  
  .nav-buttons {
    gap: var(--spacing-xs);
  }
  
  .nav-text {
    display: none; /* Hide text on small screens, keep icons */
  }
  
  main {
    padding: var(--spacing-md);
  }
  
  .content-wrapper {
    padding: var(--spacing-md);
  }
  
  .ux-info-panel {
    position: static;
    transform: none;
    margin: var(--spacing-lg) 0;
    max-width: none;
  }
}

/* Focus styles for accessibility */
*:focus-visible {
  outline: 2px solid var(--color-primary);
  outline-offset: 2px;
}

/* Reduced motion for accessibility */
@media (prefers-reduced-motion: reduce) {
  * {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}