/* ==========================================================================
   Design System for Research Page
   Clean, minimal, typography-first
   ========================================================================== */

/* CSS Variables */
:root {
  /* Colors */
  --color-bg: #ffffff;
  --color-bg-secondary: #f5f5f7;
  --color-text-primary: #1d1d1f;
  --color-text-secondary: #86868b;
  --color-accent: #0071e3;
  --color-accent-hover: #0077ed;
  --color-border: #d2d2d7;
  --color-border-light: #e8e8ed;

  /* Typography */
  --font-sans: -apple-system, BlinkMacSystemFont, 'SF Pro Display', 'SF Pro Text', 'Helvetica Neue', Helvetica, Arial, sans-serif;

  /* Spacing */
  --spacing-xs: 0.5rem;
  --spacing-sm: 1rem;
  --spacing-md: 1.5rem;
  --spacing-lg: 2rem;
  --spacing-xl: 3rem;
  --spacing-2xl: 4rem;
  --spacing-3xl: 6rem;

  /* Layout */
  --max-width: 980px;
  --nav-height: 48px;

  /* Transitions */
  --transition-fast: 0.15s ease;
  --transition-normal: 0.3s ease;

  /* Border Radius */
  --radius-sm: 8px;
  --radius-md: 12px;
}

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

html {
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  margin: 0;
  padding: 0;
  font-family: var(--font-sans);
  font-size: 1rem;
  line-height: 1.5;
  color: var(--color-text-primary);
  background-color: var(--color-bg);
}

/* Typography */
h1, h2, h3, h4 {
  margin: 0 0 var(--spacing-md);
  font-weight: 600;
  line-height: 1.1;
  letter-spacing: -0.02em;
  color: var(--color-text-primary);
}

h1 {
  font-size: 3rem;
  font-weight: 700;
  letter-spacing: -0.03em;
}

h2 {
  font-size: 2rem;
}

h3 {
  font-size: 1.5rem;
}

h4 {
  font-size: 1.25rem;
}

p {
  margin: 0 0 var(--spacing-md);
  color: var(--color-text-secondary);
  line-height: 1.6;
}

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

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

/* Navigation */
.nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--nav-height);
  background: rgba(255, 255, 255, 0.8);
  backdrop-filter: saturate(180%) blur(20px);
  -webkit-backdrop-filter: saturate(180%) blur(20px);
  border-bottom: 1px solid var(--color-border-light);
  z-index: 1000;
}

.nav-container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--spacing-lg);
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.nav-logo {
  font-size: 1.125rem;
  font-weight: 600;
  color: var(--color-text-primary);
  text-decoration: none;
}

.nav-logo:hover {
  color: var(--color-text-primary);
}

.nav-links {
  display: flex;
  gap: var(--spacing-lg);
  align-items: center;
}

.nav-link {
  font-size: 0.875rem;
  color: var(--color-text-secondary);
  text-decoration: none;
  transition: color var(--transition-fast);
}

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

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

/* Main Content */
.main {
  padding-top: calc(var(--nav-height) + var(--spacing-3xl));
  padding-bottom: var(--spacing-3xl);
}

.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--spacing-lg);
}

/* Page Header */
.page-header {
  margin-bottom: var(--spacing-2xl);
}

.page-title {
  font-size: 2.5rem;
  font-weight: 700;
  margin-bottom: var(--spacing-sm);
}

.page-description {
  font-size: 1.125rem;
  color: var(--color-text-secondary);
  max-width: 600px;
}

/* Project Cards */
.project-card {
  background: var(--color-bg);
  border: 1px solid var(--color-border-light);
  border-radius: var(--radius-md);
  padding: var(--spacing-xl);
  margin-bottom: var(--spacing-lg);
  transition: box-shadow var(--transition-normal), border-color var(--transition-normal);
}

.project-card:hover {
  border-color: var(--color-border);
  box-shadow: 0 8px 30px rgba(0, 0, 0, 0.06);
}

.project-header {
  margin-bottom: var(--spacing-md);
}

.project-title {
  font-size: 1.375rem;
  font-weight: 600;
  margin-bottom: var(--spacing-xs);
  color: var(--color-text-primary);
}

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

.project-description {
  font-size: 1rem;
  color: var(--color-text-secondary);
  line-height: 1.6;
  margin-bottom: var(--spacing-md);
}

.project-highlights {
  list-style: none;
  padding: 0;
  margin: 0 0 var(--spacing-md);
}

.project-highlights li {
  position: relative;
  padding-left: var(--spacing-md);
  font-size: 0.9375rem;
  color: var(--color-text-secondary);
  margin-bottom: var(--spacing-xs);
}

.project-highlights li::before {
  content: '';
  position: absolute;
  left: 0;
  top: 0.6em;
  width: 5px;
  height: 5px;
  background: var(--color-accent);
  border-radius: 50%;
}

.project-links {
  display: flex;
  gap: var(--spacing-sm);
}

.project-link {
  display: inline-flex;
  align-items: center;
  gap: var(--spacing-xs);
  padding: var(--spacing-xs) var(--spacing-sm);
  font-size: 0.875rem;
  color: var(--color-accent);
  background: rgba(0, 113, 227, 0.08);
  border-radius: var(--radius-sm);
  transition: background var(--transition-fast);
}

.project-link:hover {
  background: rgba(0, 113, 227, 0.15);
  color: var(--color-accent);
}

/* Footer */
.footer {
  padding: var(--spacing-xl) 0;
  text-align: center;
  border-top: 1px solid var(--color-border-light);
}

.footer p {
  font-size: 0.875rem;
  color: var(--color-text-secondary);
  margin: 0;
}

/* Utility Classes */
.mb-sm {
  margin-bottom: var(--spacing-sm);
}

/* Responsive Design */
@media (max-width: 768px) {
  :root {
    --spacing-3xl: 4rem;
  }

  .nav-links {
    gap: var(--spacing-sm);
  }

  .nav-link {
    font-size: 0.8125rem;
  }

  h1 {
    font-size: 2rem;
  }

  h2 {
    font-size: 1.5rem;
  }

  .page-title {
    font-size: 2rem;
  }
}

@media (max-width: 480px) {
  .container {
    padding: 0 var(--spacing-md);
  }

  .project-card {
    padding: var(--spacing-lg);
  }
}