/* ==========================================================================
   PERSONAL LABORATORY & ARCHIVE - DESIGN SYSTEM & CORE STYLES
   Electrical Engineering Undergraduate Portfolio
   ========================================================================== */

/* --------------------------------------------------------------------------
   1. CSS Custom Properties / Color Themes
   -------------------------------------------------------------------------- */
:root {
  /* Color Palette - Light Mode (Warm Ceramic & High-Contrast Obsidian) */
  --bg-primary: #FBFBF9;
  --bg-secondary: #F3F3F0;
  --bg-surface: #FFFFFF;
  --bg-surface-hover: #F8F9FA;
  
  --text-primary: #181A1B;
  --text-secondary: #4A5568;
  --text-muted: #718096;
  --text-inverse: #FFFFFF;
  
  --border-color: #E2E8F0;
  --border-hover: #CBD5E0;
  
  --accent-color: #0F52BA; /* Sapphire/Cobalt RF Blue */
  --accent-hover: #0A3C8A;
  --accent-subtle: rgba(15, 82, 186, 0.08);
  
  --tag-bg: #EDF2F7;
  --tag-text: #2D3748;
  
  --status-active: #10B981;
  --status-active-bg: rgba(16, 185, 129, 0.1);
  
  /* Typography */
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', 'Cascadia Code', Consolas, monospace;
  --font-heading: 'Outfit', 'Plus Jakarta Sans', var(--font-sans);
  
  /* Layout & Spacing */
  --max-width: 1120px;
  --reading-width: 720px;
  --header-height: 72px;
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.05);
  --shadow-md: 0 4px 12px rgba(0,0,0,0.08);
  --transition: all 0.2s cubic-bezier(0.16, 1, 0.3, 1);
}

/* Dark Mode Palette (Deep Technical Slate / Obsidian) */
[data-theme="dark"] {
  --bg-primary: #0D1117;
  --bg-secondary: #161B22;
  --bg-surface: #1C2128;
  --bg-surface-hover: #22272E;
  
  --text-primary: #F0F6FC;
  --text-secondary: #8B949E;
  --text-muted: #6E7681;
  --text-inverse: #0D1117;
  
  --border-color: #30363D;
  --border-hover: #444C56;
  
  --accent-color: #58A6FF;
  --accent-hover: #79C0FF;
  --accent-subtle: rgba(88, 166, 255, 0.12);
  
  --tag-bg: #21262D;
  --tag-text: #C9D1D9;
  
  --status-active: #3FB950;
  --status-active-bg: rgba(63, 185, 80, 0.15);
  
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.3);
  --shadow-md: 0 4px 16px rgba(0,0,0,0.4);
}

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

html {
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.6;
  color: var(--text-primary);
  background-color: var(--bg-primary);
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

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

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

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

button, input, textarea {
  font-family: inherit;
  font-size: inherit;
}

/* Accessibility Focus Ring */
:focus-visible {
  outline: 2px solid var(--accent-color);
  outline-offset: 3px;
}

/* Respect Reduced Motion */
@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;
  }
}

/* --------------------------------------------------------------------------
   3. Container & Layout Utilities
   -------------------------------------------------------------------------- */
.container {
  width: 100%;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 1.5rem;
}

.reading-container {
  width: 100%;
  max-width: var(--reading-width);
  margin: 0 auto;
  padding: 0 1.5rem;
}

.main-content {
  flex: 1;
  padding-top: calc(var(--header-height) + 2rem);
  padding-bottom: 5rem;
}

.section-spacing {
  margin-bottom: 4.5rem;
}

.grid-2 {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 1.5rem;
}

.grid-3 {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1.5rem;
}

/* --------------------------------------------------------------------------
   4. Header & Navigation
   -------------------------------------------------------------------------- */
.site-header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--header-height);
  background-color: rgba(251, 251, 249, 0.85);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border-color);
  z-index: 1000;
  transition: background-color 0.3s ease, border-color 0.3s ease;
}

[data-theme="dark"] .site-header {
  background-color: rgba(13, 17, 23, 0.85);
}

.nav-container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
}

.site-brand {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  font-weight: 700;
  font-size: 1.125rem;
  color: var(--text-primary);
  letter-spacing: -0.02em;
}

.brand-badge {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  font-weight: 500;
  padding: 0.15rem 0.45rem;
  background-color: var(--accent-subtle);
  color: var(--accent-color);
  border-radius: var(--radius-sm);
  border: 1px solid rgba(15, 82, 186, 0.2);
}

.nav-menu {
  display: flex;
  align-items: center;
  gap: 1.75rem;
  list-style: none;
}

.nav-link {
  font-size: 0.9375rem;
  font-weight: 500;
  color: var(--text-secondary);
  transition: var(--transition);
  position: relative;
  padding: 0.3rem 0;
}

.nav-link:hover, .nav-link.active {
  color: var(--text-primary);
}

.nav-link.active::after {
  content: '';
  position: absolute;
  bottom: -2px;
  left: 0;
  right: 0;
  height: 2px;
  background-color: var(--accent-color);
  border-radius: 1px;
}

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

.theme-toggle {
  background: none;
  border: 1px solid var(--border-color);
  color: var(--text-secondary);
  width: 38px;
  height: 38px;
  border-radius: var(--radius-md);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: var(--transition);
}

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

.mobile-menu-btn {
  display: none;
  background: none;
  border: 1px solid var(--border-color);
  color: var(--text-primary);
  width: 38px;
  height: 38px;
  border-radius: var(--radius-md);
  cursor: pointer;
  align-items: center;
  justify-content: center;
}

/* --------------------------------------------------------------------------
   5. Headings & Typography Elements
   -------------------------------------------------------------------------- */
h1, h2, h3, h4, h5, h6 {
  color: var(--text-primary);
  font-family: var(--font-heading);
  letter-spacing: -0.02em;
  line-height: 1.25;
}

.page-header {
  margin-bottom: 3rem;
  border-bottom: 1px solid var(--border-color);
  padding-bottom: 2rem;
}

.page-title {
  font-size: 2.5rem;
  font-weight: 800;
  margin-bottom: 0.75rem;
}

.page-subtitle {
  font-size: 1.125rem;
  color: var(--text-secondary);
  max-width: 680px;
}

.section-title {
  font-size: 1.5rem;
  font-weight: 700;
  margin-bottom: 1.5rem;
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.section-title::before {
  content: '';
  display: inline-block;
  width: 8px;
  height: 18px;
  background-color: var(--accent-color);
  border-radius: 2px;
}

.mono-tag {
  font-family: var(--font-mono);
  font-size: 0.8125rem;
  color: var(--accent-color);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  margin-bottom: 0.5rem;
  display: block;
}

/* --------------------------------------------------------------------------
   6. Buttons & Interactive Elements
   -------------------------------------------------------------------------- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  padding: 0.65rem 1.25rem;
  font-size: 0.9375rem;
  font-weight: 600;
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: var(--transition);
  border: 1px solid transparent;
  white-space: nowrap;
}

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

.btn-primary:hover {
  background-color: var(--accent-hover);
  color: #FFFFFF;
  transform: translateY(-1px);
  box-shadow: var(--shadow-sm);
}

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

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

.btn-icon {
  width: 18px;
  height: 18px;
  fill: currentColor;
}

/* --------------------------------------------------------------------------
   7. Cards & Modules Design System
   -------------------------------------------------------------------------- */
.card {
  background-color: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: 1.5rem;
  transition: var(--transition);
  display: flex;
  flex-direction: column;
}

.card:hover {
  border-color: var(--border-hover);
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
}

.card-title {
  font-size: 1.25rem;
  font-weight: 700;
  margin-bottom: 0.5rem;
}

.card-meta {
  font-family: var(--font-mono);
  font-size: 0.8125rem;
  color: var(--text-muted);
  margin-bottom: 0.75rem;
  display: flex;
  align-items: center;
  gap: 1rem;
  flex-wrap: wrap;
}

.card-body {
  color: var(--text-secondary);
  font-size: 0.95rem;
  margin-bottom: 1.25rem;
  flex: 1;
}

.tag-list {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.tag {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  padding: 0.2rem 0.55rem;
  background-color: var(--tag-bg);
  color: var(--tag-text);
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-color);
}

/* --------------------------------------------------------------------------
   8. HERO SECTION
   -------------------------------------------------------------------------- */
.hero-section {
  display: grid;
  grid-template-columns: 240px 1fr;
  gap: 3rem;
  align-items: center;
  padding: 2.5rem 0 3.5rem 0;
  border-bottom: 1px solid var(--border-color);
  margin-bottom: 3.5rem;
}

.hero-avatar-wrapper {
  position: relative;
}

.hero-avatar {
  width: 220px;
  height: 220px;
  border-radius: 50%;
  object-fit: cover;
  border: 3px solid var(--bg-surface);
  box-shadow: 0 0 0 1px var(--border-color), var(--shadow-md);
  background-color: var(--bg-secondary);
}

.hero-title {
  font-size: 2.75rem;
  font-weight: 800;
  letter-spacing: -0.03em;
  margin-bottom: 0.35rem;
}

.hero-subtitle {
  font-family: var(--font-mono);
  font-size: 1.05rem;
  color: var(--accent-color);
  font-weight: 600;
  margin-bottom: 1rem;
}

.hero-description {
  font-size: 1.125rem;
  color: var(--text-secondary);
  max-width: 680px;
  margin-bottom: 1.75rem;
  line-height: 1.7;
}

.hero-actions {
  display: flex;
  gap: 1rem;
  flex-wrap: wrap;
}

/* --------------------------------------------------------------------------
   9. "CURRENTLY" DASHBOARD BOARD
   -------------------------------------------------------------------------- */
.currently-box {
  background-color: var(--bg-surface);
  border: 1px solid var(--border-color);
  border-radius: var(--radius-lg);
  padding: 1.75rem;
  margin-bottom: 3.5rem;
}

.currently-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 1.25rem;
  padding-bottom: 0.75rem;
  border-bottom: 1px solid var(--border-color);
}

.currently-title {
  font-family: var(--font-mono);
  font-size: 0.875rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  display: flex;
  align-items: center;
  gap: 0.6rem;
}

.status-dot {
  width: 9px;
  height: 9px;
  background-color: var(--status-active);
  border-radius: 50%;
  box-shadow: 0 0 0 3px var(--status-active-bg);
}

.currently-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 1.25rem;
}

.currently-item {
  display: flex;
  flex-direction: column;
}

.currently-label {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--text-muted);
  text-transform: uppercase;
  margin-bottom: 0.25rem;
}

.currently-value {
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--text-primary);
}

/* --------------------------------------------------------------------------
   10. RESEARCH INTERESTS GRID
   -------------------------------------------------------------------------- */
.research-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 1.25rem;
}

.research-item {
  background-color: var(--bg-surface);
  border: 1px solid var(--border-color);
  padding: 1.25rem;
  border-radius: var(--radius-md);
  transition: var(--transition);
}

.research-item:hover {
  border-color: var(--accent-color);
  background-color: var(--accent-subtle);
}

.research-item-title {
  font-size: 1.05rem;
  font-weight: 700;
  margin-bottom: 0.35rem;
}

.research-item-desc {
  font-size: 0.875rem;
  color: var(--text-secondary);
}

/* --------------------------------------------------------------------------
   11. TIMELINE COMPONENT (Education & Experience)
   -------------------------------------------------------------------------- */
.timeline {
  position: relative;
  padding-left: 2rem;
}

.timeline::before {
  content: '';
  position: absolute;
  left: 7px;
  top: 8px;
  bottom: 8px;
  width: 2px;
  background-color: var(--border-color);
}

.timeline-item {
  position: relative;
  margin-bottom: 2.5rem;
}

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

.timeline-dot {
  position: absolute;
  left: -2rem;
  top: 6px;
  width: 16px;
  height: 16px;
  border-radius: 50%;
  background-color: var(--bg-primary);
  border: 3px solid var(--accent-color);
}

.timeline-date {
  font-family: var(--font-mono);
  font-size: 0.8125rem;
  color: var(--accent-color);
  font-weight: 600;
  margin-bottom: 0.25rem;
}

.timeline-title {
  font-size: 1.25rem;
  font-weight: 700;
  margin-bottom: 0.25rem;
}

.timeline-subtitle {
  font-size: 1rem;
  color: var(--text-secondary);
  margin-bottom: 0.75rem;
  font-weight: 500;
}

.timeline-body {
  color: var(--text-secondary);
  font-size: 0.95rem;
}

/* --------------------------------------------------------------------------
   12. JOURNAL ARTICLE LAYOUT
   -------------------------------------------------------------------------- */
.article-header {
  margin-bottom: 2.5rem;
  border-bottom: 1px solid var(--border-color);
  padding-bottom: 2rem;
}

.article-meta {
  display: flex;
  align-items: center;
  gap: 1.25rem;
  font-family: var(--font-mono);
  font-size: 0.85rem;
  color: var(--text-muted);
  margin-bottom: 1rem;
}

.article-title {
  font-size: 2.5rem;
  font-weight: 800;
  line-height: 1.2;
  margin-bottom: 1rem;
}

.article-content {
  font-size: 1.0625rem;
  line-height: 1.8;
  color: var(--text-primary);
}

.article-content p {
  margin-bottom: 1.5rem;
}

.article-content h2 {
  font-size: 1.65rem;
  margin-top: 2.5rem;
  margin-bottom: 1rem;
}

.article-content h3 {
  font-size: 1.3rem;
  margin-top: 2rem;
  margin-bottom: 0.75rem;
}

.article-content blockquote {
  border-left: 3px solid var(--accent-color);
  padding-left: 1.25rem;
  margin: 1.75rem 0;
  font-style: italic;
  color: var(--text-secondary);
}

.article-content code {
  font-family: var(--font-mono);
  font-size: 0.9em;
  background-color: var(--bg-secondary);
  padding: 0.15em 0.4em;
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-color);
}

/* --------------------------------------------------------------------------
   13. FOOTER
   -------------------------------------------------------------------------- */
.site-footer {
  background-color: var(--bg-secondary);
  border-top: 1px solid var(--border-color);
  padding: 3rem 0;
  margin-top: auto;
}

.footer-container {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 2rem;
  flex-wrap: wrap;
}

.footer-brand-title {
  font-weight: 700;
  font-size: 1.1rem;
  margin-bottom: 0.5rem;
}

.footer-brand-desc {
  font-size: 0.875rem;
  color: var(--text-muted);
  max-width: 320px;
}

.footer-links {
  display: flex;
  gap: 3rem;
  flex-wrap: wrap;
}

.footer-column-title {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  color: var(--text-muted);
  margin-bottom: 0.75rem;
}

.footer-nav {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.footer-link {
  font-size: 0.875rem;
  color: var(--text-secondary);
}

.footer-link:hover {
  color: var(--text-primary);
}

.footer-bottom {
  margin-top: 2.5rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--border-color);
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 0.8125rem;
  color: var(--text-muted);
  flex-wrap: wrap;
  gap: 1rem;
}