/* ===================================
   Core Design Tokens
   =================================== */
:root {
  /* Core Palette */
  --color-surface: #ffffff;
  --color-background: #ffffff;
  --color-text-primary: #0f172a;
  --color-text-secondary: rgba(15, 23, 42, 0.7);
  --color-text-muted: rgba(15, 23, 42, 0.5);
  --color-accent: #2563eb;

  /* Derived Tokens */
  --color-border: rgba(15, 23, 42, 0.08);
  --color-border-strong: rgba(15, 23, 42, 0.16);
  --color-accent-soft: rgba(37, 99, 235, 0.1);
  --color-shadow: rgba(15, 23, 42, 0.06);
  --color-shadow-hover: rgba(15, 23, 42, 0.12);

  /* Typography */
  --font-family: 'Inter', 'Pretendard', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
  --font-size-base: 16px;
  --font-size-small: 14px;
  --font-size-large: 18px;
  --font-size-xl: 24px;
  --font-size-xxl: 48px;
  --line-height-base: 1.6;

  /* Spacing */
  --spacing-xs: 8px;
  --spacing-sm: 16px;
  --spacing-md: 24px;
  --spacing-lg: 32px;
  --spacing-xl: 48px;
  --spacing-xxl: 80px;
  --spacing-xxxl: 120px;

  /* Layout */
  --container-max-width: 1200px;
  --border-radius: 16px;
  --transition-speed: 0.3s;
}

/* ===================================
   Base Styles
   =================================== */
* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-family);
  font-size: var(--font-size-base);
  line-height: var(--line-height-base);
  color: var(--color-text-primary);
  background-color: var(--color-background);
  margin: 0;
  padding: 0;
  -webkit-font-smoothing: antialiased;
}

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

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

a:hover {
  color: rgba(37, 99, 235, 0.82);
}

/* ===================================
   Typography
   =================================== */
h1, h2, h3, h4, h5, h6 {
  margin: 0 0 var(--spacing-md) 0;
  font-weight: 700;
  line-height: 1.2;
  color: var(--color-text-primary);
}

h1 {
  font-size: var(--font-size-xxl);
  font-weight: 800;
}

h2 {
  font-size: 2.5rem;
  font-weight: 700;
}

h3 {
  font-size: 1.75rem;
}

h4 {
  font-size: 1.25rem;
}

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

/* Text Gradient Effect */
.text-gradient {
  background: linear-gradient(135deg, rgba(37, 99, 235, 1) 0%, rgba(37, 99, 235, 0.65) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

/* ===================================
   Layout Components
   =================================== */
.container {
  max-width: var(--container-max-width);
  margin: 0 auto;
  padding: 0 var(--spacing-md);
}

.section {
  padding: var(--spacing-xxl) 0;
}

.section-light {
  background: linear-gradient(180deg, rgba(37, 99, 235, 0.05) 0%, rgba(37, 99, 235, 0) 100%);
}

/* ===================================
   Header & Navigation
   =================================== */
.header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  background-color: rgba(255, 255, 255, 0.9);
  backdrop-filter: blur(18px);
  border-bottom: 1px solid var(--color-border);
  box-shadow: 0 8px 24px rgba(15, 23, 42, 0.05);
  z-index: 1000;
  transition: transform var(--transition-speed), box-shadow var(--transition-speed);
}

.header-container {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: var(--spacing-md) var(--spacing-lg);
}

.logo {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--color-text-primary);
  letter-spacing: -0.5px;
}

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

.nav-link {
  color: var(--color-text-secondary);
  font-weight: 500;
  padding: var(--spacing-xs) var(--spacing-sm);
  border-radius: 999px;
  transition: background-color var(--transition-speed), color var(--transition-speed);
}

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

.mobile-menu-toggle {
  display: none;
  background: none;
  border: none;
  font-size: 1.5rem;
  cursor: pointer;
  color: var(--color-text-primary);
}

/* Mobile Navigation */
@media (max-width: 768px) {
  .mobile-menu-toggle {
    display: block;
  }

  .nav {
    position: fixed;
    top: 70px;
    left: 0;
    right: 0;
    flex-direction: column;
    background-color: var(--color-surface);
    padding: var(--spacing-md);
    border-bottom: 1px solid var(--color-border);
    transform: translateY(-100%);
    opacity: 0;
    pointer-events: none;
    transition: transform var(--transition-speed), opacity var(--transition-speed);
  }

  .nav.active {
    transform: translateY(0);
    opacity: 1;
    pointer-events: all;
  }
}

/* ===================================
   Buttons
   =================================== */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--spacing-xs);
  padding: 14px 30px;
  font-size: var(--font-size-base);
  font-weight: 600;
  text-align: center;
  border-radius: 999px;
  border: 1px solid transparent;
  cursor: pointer;
  transition: transform var(--transition-speed), box-shadow var(--transition-speed), background-color var(--transition-speed);
  text-decoration: none;
  min-width: 44px;
  min-height: 44px;
}

.btn-primary {
  background: var(--color-accent);
  color: #fff;
  box-shadow: 0 12px 24px rgba(37, 99, 235, 0.2);
}

.btn-primary:hover {
  transform: translateY(-2px);
  box-shadow: 0 18px 32px rgba(37, 99, 235, 0.24);
}

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

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

.btn-large {
  padding: 18px 42px;
  font-size: var(--font-size-large);
}

/* ===================================
   Hero Section
   =================================== */
.hero {
  min-height: 50vh;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  /* padding-top: calc(72px + var(--spacing-xl)); */
  /* padding-bottom: var(--spacing-xl); */
  position: relative;
  overflow: hidden;
  background: radial-gradient(circle at 20% 20%, rgba(37, 99, 235, 0.12), transparent 55%),
              radial-gradient(circle at 80% 0%, rgba(37, 99, 235, 0.14), transparent 60%),
              var(--color-background);
}

.hero::after {
  content: '';
  position: absolute;
  inset: 0;
  background: linear-gradient(180deg, rgba(255, 255, 255, 0.85) 0%, rgba(255, 255, 255, 0.95) 100%);
  z-index: 0;
}

.hero .container {
  position: relative;
  z-index: 1;
}

.hero-title {
  font-size: clamp(2.75rem, 8vw, 4.25rem);
  margin-bottom: var(--spacing-lg);
  font-weight: 800;
  line-height: 1.1;
  color: var(--color-text-primary);
  letter-spacing: -0.02em;
}

.hero-subtitle {
  font-size: clamp(1.05rem, 2.6vw, 1.35rem);
  margin-bottom: var(--spacing-xl);
  color: var(--color-text-secondary);
  max-width: 820px;
  margin-left: auto;
  margin-right: auto;
  line-height: 1.75;
}

.hero-cta {
  display: flex;
  gap: var(--spacing-md);
  justify-content: center;
  flex-wrap: wrap;
  margin-top: var(--spacing-xl);
}

/* ===================================
   About/Company Section
   =================================== */
.about-grid {
  display: grid;
  grid-template-columns: 1.1fr 0.9fr;
  gap: var(--spacing-xxl);
  align-items: center;
  margin-top: var(--spacing-xl);
}

.about-content p {
  font-size: var(--font-size-large);
  margin-bottom: var(--spacing-md);
  line-height: 1.8;
}

.about-stats {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: var(--spacing-lg);
  margin-top: var(--spacing-xl);
}

.stat-item {
  padding: var(--spacing-lg);
  background-color: var(--color-surface);
  border-radius: var(--border-radius);
  border: 1px solid var(--color-border);
  box-shadow: 0 10px 30px var(--color-shadow);
}

.stat-number {
  font-size: 2.5rem;
  font-weight: 700;
  color: var(--color-text-primary);
  display: block;
  margin-bottom: var(--spacing-xs);
}

.stat-label {
  color: var(--color-text-muted);
  font-size: var(--font-size-small);
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

@media (max-width: 768px) {
  .about-grid {
    grid-template-columns: 1fr;
    gap: var(--spacing-lg);
  }

  .about-stats {
    grid-template-columns: 1fr;
  }
}

/* ===================================
   Projects/Services Section
   =================================== */
.projects-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  gap: var(--spacing-lg);
  margin-top: var(--spacing-xl);
}

.project-card {
  background-color: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: calc(var(--border-radius) + 4px);
  overflow: hidden;
  transition: transform var(--transition-speed), box-shadow var(--transition-speed), border-color var(--transition-speed);
  cursor: pointer;
  box-shadow: 0 16px 40px rgba(15, 23, 42, 0.05);
}

.project-card:hover {
  transform: translateY(-6px);
  box-shadow: 0 24px 50px rgba(15, 23, 42, 0.08);
  border-color: var(--color-border-strong);
}

.project-image {
  width: 100%;
  height: 220px;
  background: radial-gradient(circle at 20% 20%, rgba(37, 99, 235, 0.15), transparent 65%),
              linear-gradient(135deg, rgba(37, 99, 235, 0.12), rgba(37, 99, 235, 0.04));
}

.project-content {
  padding: var(--spacing-xl);
}

.project-category {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 6px 14px;
  background-color: var(--color-accent-soft);
  color: var(--color-accent);
  border-radius: 999px;
  font-size: var(--font-size-small);
  font-weight: 600;
  letter-spacing: 0.02em;
  margin-bottom: var(--spacing-sm);
}

.project-title {
  font-size: 1.5rem;
  margin-bottom: var(--spacing-sm);
  color: var(--color-text-primary);
}

.project-description {
  color: var(--color-text-secondary);
  margin-bottom: var(--spacing-md);
}

.project-link {
  display: inline-flex;
  align-items: center;
  gap: var(--spacing-xs);
  color: var(--color-text-primary);
  font-weight: 600;
}

.project-link::after {
  content: '→';
  transition: transform var(--transition-speed);
  color: var(--color-accent);
}

.project-card:hover .project-link::after {
  transform: translateX(6px);
}

@media (max-width: 768px) {
  .projects-grid {
    grid-template-columns: 1fr;
  }
}

/* ===================================
   Experience Section
   =================================== */

.experience-timeline {
  max-width: 920px;
  margin: var(--spacing-xl) auto 0;
  position: relative;
  display: grid;
  gap: var(--spacing-xl);
}

.experience-item {
  display: grid;
  grid-template-columns: 120px 1fr;
  gap: var(--spacing-lg);
  align-items: start;
  padding: var(--spacing-lg);
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: calc(var(--border-radius) + 4px);
  box-shadow: 0 12px 40px rgba(15, 23, 42, 0.06);
}

.experience-logo {
  width: 64px;
  height: 64px;
  border-radius: 20px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.5rem;
  background: linear-gradient(135deg, rgba(37, 99, 235, 0.12), rgba(37, 99, 235, 0.04));
  border: 1px solid var(--color-border);
  color: var(--color-accent);
}

.experience-content {
  padding: 0;
}

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

.experience-title {
  font-size: 1.5rem;
  margin: 0;
}


.experience-period {
  color: var(--color-text-muted);
  font-size: var(--font-size-small);
  white-space: nowrap;
}

.experience-company {
  color: var(--color-accent);
  font-weight: 600;
  margin-bottom: var(--spacing-xs);
}

.experience-description {
  color: var(--color-text-secondary);
  line-height: 1.8;
}

@media (max-width: 768px) {
  .experience-item {
    grid-template-columns: 1fr;
    text-align: left;
  }

  .experience-logo {
    width: 56px;
    height: 56px;
    font-size: 1.3rem;
  }
}

/* ===================================
   Tech Stack / Skills Section
   =================================== */
.tech-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
  gap: var(--spacing-md);
  margin-top: var(--spacing-xl);
}


.tech-item {
  background-color: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: calc(var(--border-radius) + 2px);
  padding: var(--spacing-md);
  text-align: left;
  transition: transform var(--transition-speed), box-shadow var(--transition-speed);
  box-shadow: 0 10px 30px rgba(15, 23, 42, 0.05);
}

.tech-item:hover {
  transform: translateY(-4px);
  box-shadow: 0 18px 40px rgba(15, 23, 42, 0.08);
}

.tech-icon {
  font-size: 2rem;
  margin-bottom: var(--spacing-xs);
}

.tech-name {
  font-weight: 600;
  color: var(--color-text-primary);
}

/* ===================================
   Contact Section
   =================================== */
.contact-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: var(--spacing-lg);
  margin-top: var(--spacing-xl);
}

.contact-card {
  background-color: var(--color-surface);
  padding: var(--spacing-xl);
  border-radius: calc(var(--border-radius) + 4px);
  border: 1px solid var(--color-border);
  box-shadow: 0 16px 40px rgba(15, 23, 42, 0.05);
  display: flex;
  flex-direction: column;
  gap: var(--spacing-sm);
  min-height: 220px;
}

.contact-card-title {
  margin: 0;
  font-size: 1.25rem;
  color: var(--color-text-primary);
}

.contact-card-body {
  margin: 0;
  font-size: var(--font-size-large);
  color: var(--color-text-primary);
  font-weight: 600;
}

.contact-card-foot {
  margin-top: auto;
  color: var(--color-text-muted);
  font-size: var(--font-size-small);
  line-height: 1.6;
}

.contact-link {
  color: var(--color-text-primary);
  font-weight: 600;
  display: inline-flex;
  align-items: center;
  gap: 6px;
}

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

@media (max-width: 768px) {
  .contact-card {
    min-height: auto;
  }
}

@media (max-width: 600px) {
  .section {
    padding: var(--spacing-lg) 0;
  }

  .header-container {
    padding: var(--spacing-sm) var(--spacing-md);
  }

  .hero {
    min-height: auto;
    padding-top: calc(64px + var(--spacing-lg));
    padding-bottom: var(--spacing-xl);
  }

  .hero-subtitle {
    font-size: 1rem;
    line-height: 1.6;
  }

  .hero-cta {
    width: 100%;
    gap: var(--spacing-sm);
  }

  .btn-large,
  .btn {
    width: 100%;
  }

  .about-grid {
    gap: var(--spacing-md);
  }

  .stat-item {
    padding: var(--spacing-md);
    text-align: center;
  }

  .projects-grid {
    gap: var(--spacing-md);
  }

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

  .experience-item {
    padding: var(--spacing-lg);
    gap: var(--spacing-md);
  }

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

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

  .footer-content {
    gap: var(--spacing-lg);
  }
}

/* ===================================
   Footer
   =================================== */

.footer {
  background: linear-gradient(180deg, rgba(37, 99, 235, 0.04) 0%, rgba(37, 99, 235, 0.07) 100%);
  border-top: 1px solid var(--color-border);
  padding: var(--spacing-xxl) 0 var(--spacing-lg) 0;
}

.footer-content {
  display: grid;
  grid-template-columns: 2fr 1fr 1fr 1fr;
  gap: var(--spacing-xxl);
  margin-bottom: var(--spacing-xl);
}

.footer-section h3 {
  color: var(--color-text-primary);
  margin-bottom: var(--spacing-md);
  font-size: 1.25rem;
}

.footer-section p {
  color: var(--color-text-secondary);
}

.footer-links {
  list-style: none;
  padding: 0;
  margin: 0;
}

.footer-links li {
  margin-bottom: var(--spacing-sm);
}

.footer-links a {
  color: var(--color-text-secondary);
  transition: color var(--transition-speed);
}

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

.footer-bottom {
  text-align: center;
  padding-top: var(--spacing-lg);
  border-top: 1px solid var(--color-border);
  color: var(--color-text-muted);
}

@media (max-width: 768px) {
  .footer-content {
    grid-template-columns: 1fr;
    gap: var(--spacing-lg);
  }
}

/* ===================================
   Utility Classes
   =================================== */
.text-center {
  text-align: center;
}

.mt-lg {
  margin-top: var(--spacing-lg);
}

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

/* Accessibility */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

/* Focus styles for keyboard navigation */
a:focus,
button:focus,
input:focus,
textarea:focus {
  outline: 2px solid var(--color-accent);
  outline-offset: 2px;
}

/* ===================================
   Animations
   =================================== */
@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.fade-in {
  animation: fadeIn 0.6s ease-out;
}

/* ===================================
   Scrollbar Styling (Optional)
   =================================== */
::-webkit-scrollbar {
  width: 12px;
}

::-webkit-scrollbar-track {
  background: var(--color-background);
}

::-webkit-scrollbar-thumb {
  background: rgba(15, 23, 42, 0.2);
  border-radius: 6px;
}

::-webkit-scrollbar-thumb:hover {
  background: rgba(15, 23, 42, 0.3);
}