/* ==========================================================================
   Professional Personal Website - Main Stylesheet
   Clean, minimal design with subtle modern flair
   ========================================================================== */

/* --------------------------------------------------------------------------
   CSS Custom Properties (Design Tokens)
   -------------------------------------------------------------------------- */
:root {
  /* Colors - Professional neutral palette with deep blue accent */
  --color-bg: #fafafa;
  --color-bg-alt: #ffffff;
  --color-text: #1a1a2e;
  --color-text-muted: #6b7280;
  --color-accent: #1e3a5f;
  --color-accent-light: #2d5a87;
  --color-border: #e5e7eb;
  --color-border-light: #f3f4f6;
  
  /* Typography */
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', monospace;
  
  /* Font Sizes */
  --text-xs: 0.75rem;
  --text-sm: 0.875rem;
  --text-base: 1rem;
  --text-lg: 1.125rem;
  --text-xl: 1.25rem;
  --text-2xl: 1.5rem;
  --text-3xl: 1.875rem;
  --text-4xl: 2.25rem;
  
  /* Spacing */
  --space-xs: 0.25rem;
  --space-sm: 0.5rem;
  --space-md: 1rem;
  --space-lg: 1.5rem;
  --space-xl: 2rem;
  --space-2xl: 3rem;
  --space-3xl: 4rem;
  
  /* Layout */
  --max-width: 900px;
  --nav-height: 64px;
  
  /* Effects */
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
  --transition-fast: 150ms ease;
  --transition-base: 250ms ease;
}

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

html {
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  font-family: var(--font-sans);
  font-size: var(--text-base);
  line-height: 1.7;
  color: var(--color-text);
  background-color: var(--color-bg);
  min-height: 100vh;
}

a {
  color: var(--color-accent);
  text-decoration: none;
  transition: color var(--transition-fast);
}

a:hover {
  color: var(--color-accent-light);
}

img {
  max-width: 100%;
  height: auto;
  display: block;
}

/* --------------------------------------------------------------------------
   Typography
   -------------------------------------------------------------------------- */
h1, h2, h3, h4, h5, h6 {
  font-weight: 600;
  line-height: 1.3;
  color: var(--color-text);
}

h1 {
  font-size: var(--text-4xl);
  letter-spacing: -0.025em;
}

h2 {
  font-size: var(--text-2xl);
  margin-bottom: var(--space-lg);
}

h3 {
  font-size: var(--text-xl);
  margin-bottom: var(--space-md);
}

p {
  margin-bottom: var(--space-md);
  color: var(--color-text-muted);
}

p:last-child {
  margin-bottom: 0;
}

/* --------------------------------------------------------------------------
   Layout Components
   -------------------------------------------------------------------------- */
.container {
  width: 100%;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--space-lg);
}

.section {
  padding: var(--space-3xl) 0;
}

.section-title {
  position: relative;
  display: inline-block;
  margin-bottom: var(--space-xl);
}

.section-title::after {
  content: '';
  position: absolute;
  bottom: -8px;
  left: 0;
  width: 40px;
  height: 3px;
  background: var(--color-accent);
  border-radius: 2px;
}

/* --------------------------------------------------------------------------
   Navigation
   -------------------------------------------------------------------------- */
.nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--nav-height);
  background: var(--color-bg-alt);
  border-bottom: 1px solid var(--color-border);
  z-index: 1000;
  display: flex;
  align-items: center;
}

.nav .container {
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.nav-brand {
  font-size: var(--text-lg);
  font-weight: 600;
  color: var(--color-text);
}

.nav-brand:hover {
  color: var(--color-accent);
}

.nav-links {
  display: flex;
  gap: var(--space-xl);
  list-style: none;
}

.nav-links a {
  font-size: var(--text-sm);
  font-weight: 500;
  color: var(--color-text-muted);
  padding: var(--space-sm) 0;
  position: relative;
}

.nav-links a::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  width: 0;
  height: 2px;
  background: var(--color-accent);
  transition: width var(--transition-base);
}

.nav-links a:hover,
.nav-links a.active {
  color: var(--color-text);
}

.nav-links a:hover::after,
.nav-links a.active::after {
  width: 100%;
}

.nav-toggle {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  padding: var(--space-sm);
}

.nav-toggle span {
  display: block;
  width: 24px;
  height: 2px;
  background: var(--color-text);
  margin: 5px 0;
  transition: var(--transition-fast);
}

/* Mobile Navigation */
@media (max-width: 768px) {
  .nav-toggle {
    display: block;
  }
  
  .nav-links {
    position: fixed;
    top: var(--nav-height);
    left: 0;
    right: 0;
    background: var(--color-bg-alt);
    flex-direction: column;
    padding: var(--space-lg);
    gap: var(--space-md);
    border-bottom: 1px solid var(--color-border);
    transform: translateY(-100%);
    opacity: 0;
    visibility: hidden;
    transition: var(--transition-base);
  }
  
  .nav-links.active {
    transform: translateY(0);
    opacity: 1;
    visibility: visible;
  }
  
  .nav-links a {
    font-size: var(--text-base);
    padding: var(--space-sm) 0;
  }
}

/* --------------------------------------------------------------------------
   Main Content
   -------------------------------------------------------------------------- */
main {
  margin-top: var(--nav-height);
}

/* Hero Section */
.hero {
  padding: var(--space-3xl) 0;
  min-height: 60vh;
  display: flex;
  align-items: center;
}

.hero-content {
  max-width: 650px;
}

.hero-greeting {
  font-size: var(--text-sm);
  font-weight: 500;
  color: var(--color-accent);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin-bottom: var(--space-md);
}

.hero-name {
  font-size: clamp(2.5rem, 5vw, 3.5rem);
  font-weight: 700;
  margin-bottom: var(--space-md);
  background: linear-gradient(135deg, var(--color-text) 0%, var(--color-accent) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero-title {
  font-size: var(--text-xl);
  color: var(--color-text-muted);
  margin-bottom: var(--space-lg);
}

.hero-bio {
  font-size: var(--text-lg);
  line-height: 1.8;
  margin-bottom: var(--space-xl);
}

.hero-links {
  display: flex;
  gap: var(--space-md);
  flex-wrap: wrap;
}

/* --------------------------------------------------------------------------
   Buttons & Links
   -------------------------------------------------------------------------- */
.btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-sm) var(--space-lg);
  font-size: var(--text-sm);
  font-weight: 500;
  border-radius: 6px;
  transition: all var(--transition-fast);
  cursor: pointer;
  border: none;
}

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

.btn-primary:hover {
  background: var(--color-accent-light);
  color: white;
  transform: translateY(-1px);
}

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

.btn-outline:hover {
  border-color: var(--color-accent);
  color: var(--color-accent);
}

.icon-link {
  display: inline-flex;
  align-items: center;
  gap: var(--space-xs);
  font-size: var(--text-sm);
  color: var(--color-text-muted);
}

.icon-link:hover {
  color: var(--color-accent);
}

/* --------------------------------------------------------------------------
   Cards
   -------------------------------------------------------------------------- */
.card {
  background: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  border-radius: 8px;
  padding: var(--space-xl);
  transition: all var(--transition-base);
}

.card:hover {
  border-color: var(--color-accent);
  box-shadow: var(--shadow-md);
}

.card-title {
  font-size: var(--text-lg);
  margin-bottom: var(--space-sm);
}

.card-subtitle {
  font-size: var(--text-sm);
  color: var(--color-accent);
  margin-bottom: var(--space-md);
}

.card-description {
  font-size: var(--text-sm);
  color: var(--color-text-muted);
}

/* Card Grid */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: var(--space-lg);
}

/* --------------------------------------------------------------------------
   Timeline (Experience/Education)
   -------------------------------------------------------------------------- */
.timeline {
  position: relative;
  padding-left: var(--space-xl);
}

.timeline::before {
  content: '';
  position: absolute;
  left: 0;
  top: 0;
  bottom: 0;
  width: 2px;
  background: var(--color-border);
}

.timeline-item {
  position: relative;
  padding-bottom: var(--space-2xl);
}

.timeline-item:last-child {
  padding-bottom: 0;
}

.timeline-item::before {
  content: '';
  position: absolute;
  left: calc(-1 * var(--space-xl) - 4px);
  top: 6px;
  width: 10px;
  height: 10px;
  border-radius: 50%;
  background: var(--color-accent);
  border: 2px solid var(--color-bg);
}

.timeline-header {
  margin-bottom: var(--space-md);
}

.timeline-title {
  font-size: var(--text-lg);
  font-weight: 600;
  margin-bottom: var(--space-xs);
}

.timeline-company {
  font-size: var(--text-base);
  color: var(--color-accent);
  margin-bottom: var(--space-xs);
}

.timeline-meta {
  font-size: var(--text-sm);
  color: var(--color-text-muted);
  display: flex;
  gap: var(--space-md);
  flex-wrap: wrap;
}

.timeline-content {
  color: var(--color-text-muted);
}

.timeline-content ul {
  list-style: none;
  padding: 0;
}

.timeline-content li {
  position: relative;
  padding-left: var(--space-lg);
  margin-bottom: var(--space-sm);
  font-size: var(--text-sm);
}

.timeline-content li::before {
  content: '→';
  position: absolute;
  left: 0;
  color: var(--color-accent);
}

/* --------------------------------------------------------------------------
   Course Categories (Education Page)
   -------------------------------------------------------------------------- */
.course-category {
  margin-bottom: var(--space-2xl);
}

.course-category-title {
  font-size: var(--text-lg);
  font-weight: 600;
  margin-bottom: var(--space-lg);
  padding-bottom: var(--space-sm);
  border-bottom: 1px solid var(--color-border);
}

.course-list {
  display: grid;
  gap: var(--space-md);
}

.course-item {
  display: flex;
  gap: var(--space-md);
  padding: var(--space-md);
  background: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  border-radius: 6px;
  transition: all var(--transition-fast);
}

.course-item:hover {
  border-color: var(--color-accent);
}

.course-code {
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  color: var(--color-accent);
  font-weight: 500;
  min-width: 70px;
}

.course-info {
  flex: 1;
}

.course-name {
  font-weight: 500;
  font-size: var(--text-sm);
  margin-bottom: var(--space-xs);
}

.course-desc {
  font-size: var(--text-xs);
  color: var(--color-text-muted);
}

.course-level {
  font-size: var(--text-xs);
  padding: 2px 8px;
  border-radius: 4px;
  background: var(--color-border-light);
  color: var(--color-text-muted);
  font-weight: 500;
}

/* --------------------------------------------------------------------------
   Project Cards (Projects Page)
   -------------------------------------------------------------------------- */
.project-card {
  background: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  border-radius: 8px;
  overflow: hidden;
  transition: all var(--transition-base);
}

.project-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-md);
  border-color: var(--color-accent);
}

.project-image {
  width: 100%;
  height: 180px;
  object-fit: cover;
  background: var(--color-border-light);
}

.project-content {
  padding: var(--space-lg);
}

.project-title {
  font-size: var(--text-lg);
  margin-bottom: var(--space-sm);
}

.project-tags {
  display: flex;
  gap: var(--space-sm);
  flex-wrap: wrap;
  margin-bottom: var(--space-md);
}

.project-tag {
  font-size: var(--text-xs);
  padding: 2px 8px;
  background: var(--color-border-light);
  border-radius: 4px;
  color: var(--color-text-muted);
}

.project-description {
  font-size: var(--text-sm);
  color: var(--color-text-muted);
}

/* --------------------------------------------------------------------------
   Footer
   -------------------------------------------------------------------------- */
.footer {
  padding: var(--space-2xl) 0;
  border-top: 1px solid var(--color-border);
  margin-top: var(--space-3xl);
}

.footer-content {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: var(--space-md);
}

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

.footer-links {
  display: flex;
  gap: var(--space-lg);
}

.footer-links a {
  font-size: var(--text-sm);
  color: var(--color-text-muted);
}

.footer-links a:hover {
  color: var(--color-accent);
}

/* --------------------------------------------------------------------------
   Utilities
   -------------------------------------------------------------------------- */
.text-muted {
  color: var(--color-text-muted);
}

.text-accent {
  color: var(--color-accent);
}

.mb-0 { margin-bottom: 0; }
.mb-sm { margin-bottom: var(--space-sm); }
.mb-md { margin-bottom: var(--space-md); }
.mb-lg { margin-bottom: var(--space-lg); }
.mb-xl { margin-bottom: var(--space-xl); }

/* --------------------------------------------------------------------------
   Page Header (for non-home pages)
   -------------------------------------------------------------------------- */
.page-header {
  padding: var(--space-2xl) 0;
  border-bottom: 1px solid var(--color-border);
  margin-bottom: var(--space-2xl);
}

.page-title {
  font-size: var(--text-3xl);
  margin-bottom: var(--space-sm);
}

.page-subtitle {
  font-size: var(--text-lg);
  color: var(--color-text-muted);
}

/* --------------------------------------------------------------------------
   Responsive Adjustments
   -------------------------------------------------------------------------- */
@media (max-width: 768px) {
  :root {
    --space-3xl: 3rem;
  }
  
  .hero {
    min-height: auto;
    padding: var(--space-2xl) 0;
  }
  
  .hero-name {
    font-size: 2rem;
  }
  
  .footer-content {
    flex-direction: column;
    text-align: center;
  }
  
  .timeline {
    padding-left: var(--space-lg);
  }
  
  .course-item {
    flex-direction: column;
    gap: var(--space-sm);
  }
  
  .course-code {
    min-width: auto;
  }
}

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

.hero-content,
.page-header,
.section {
  animation: fadeIn 0.5s ease-out;
}