/* ============================================
   PORTFOLIO — Design System & Global Styles
   ============================================ */

/* --- Google Fonts --- */
@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700&family=JetBrains+Mono:wght@400;500&display=swap');

/* --- CSS Custom Properties --- */
:root {
  --color-bg: #fafaf8;
  --color-bg-alt: #f3f3f0;
  --color-surface: #ffffff;
  --color-text: #1a1a1a;
  --color-text-secondary: #666666;
  --color-text-muted: #999999;
  --color-accent: #1a1a1a;
  --color-accent-hover: #333333;
  --color-border: #e5e5e5;
  --color-border-light: #f0f0ee;
  --color-link: #1a1a1a;
  --color-tag-bg: #f0f0ee;
  --color-tag-text: #555555;

  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --font-mono: 'JetBrains Mono', 'SF Mono', 'Fira Code', monospace;

  --fs-xs: 0.75rem;
  --fs-sm: 0.8125rem;
  --fs-base: 1rem;
  --fs-md: 1.125rem;
  --fs-lg: 1.5rem;
  --fs-xl: 2rem;
  --fs-2xl: 2.75rem;
  --fs-3xl: 3.5rem;

  --fw-light: 300;
  --fw-normal: 400;
  --fw-medium: 500;
  --fw-semibold: 600;
  --fw-bold: 700;

  --spacing-xs: 0.25rem;
  --spacing-sm: 0.5rem;
  --spacing-md: 1rem;
  --spacing-lg: 1.5rem;
  --spacing-xl: 2rem;
  --spacing-2xl: 3rem;
  --spacing-3xl: 4rem;
  --spacing-4xl: 6rem;

  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;

  --max-width: 760px;
  --nav-height: 64px;

  --transition-fast: 150ms ease;
  --transition-base: 250ms ease;
  --transition-slow: 400ms ease;

  --nav-bg: rgba(250, 250, 248, 0.85);
}

/* --- Dark Mode --- */
[data-theme="dark"] {
  --color-bg: #111111;
  --color-bg-alt: #1a1a1a;
  --color-surface: #1e1e1e;
  --color-text: #e8e8e6;
  --color-text-secondary: #a0a0a0;
  --color-text-muted: #666666;
  --color-accent: #e8e8e6;
  --color-accent-hover: #cccccc;
  --color-border: #2a2a2a;
  --color-border-light: #1f1f1f;
  --color-link: #e8e8e6;
  --color-tag-bg: #252525;
  --color-tag-text: #a0a0a0;

  --nav-bg: rgba(17, 17, 17, 0.85);
}

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

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

body {
  font-family: var(--font-sans);
  font-size: var(--fs-base);
  font-weight: var(--fw-normal);
  line-height: 1.7;
  color: var(--color-text);
  background-color: var(--color-bg);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  transition: background-color var(--transition-base), color var(--transition-base);
}

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

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

a:hover {
  opacity: 0.6;
}

ul,
ol {
  list-style: none;
}

button {
  font-family: inherit;
  cursor: pointer;
  border: none;
  background: none;
}

/* --- Navigation --- */
.nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--nav-height);
  background: var(--nav-bg);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--color-border-light);
  z-index: 1000;
  display: flex;
  align-items: center;
  justify-content: center;
}

.nav__inner {
  width: 100%;
  max-width: var(--max-width);
  padding: 0 var(--spacing-xl);
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.nav__logo {
  font-size: var(--fs-sm);
  font-weight: var(--fw-semibold);
  color: var(--color-text);
  letter-spacing: -0.02em;
  text-decoration: none;
}

.nav__logo:hover {
  opacity: 1;
}

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

.nav__link {
  font-size: var(--fs-sm);
  font-weight: var(--fw-normal);
  color: var(--color-text-muted);
  text-decoration: none;
  transition: color var(--transition-fast);
  position: relative;
}

.nav__link:hover {
  color: var(--color-text);
  opacity: 1;
}

.nav__link--active {
  color: var(--color-text);
  font-weight: var(--fw-medium);
}

.nav__link--active::after {
  content: '';
  position: absolute;
  bottom: -4px;
  left: 0;
  right: 0;
  height: 1.5px;
  background: var(--color-text);
  border-radius: 1px;
}

/* Mobile hamburger */
.nav__toggle {
  display: none;
  flex-direction: column;
  gap: 5px;
  padding: 4px;
  z-index: 1001;
}

.nav__toggle span {
  display: block;
  width: 20px;
  height: 1.5px;
  background: var(--color-text);
  transition: all var(--transition-base);
  transform-origin: center;
}

.nav__toggle.active span:nth-child(1) {
  transform: rotate(45deg) translate(4.5px, 4.5px);
}

.nav__toggle.active span:nth-child(2) {
  opacity: 0;
}

.nav__toggle.active span:nth-child(3) {
  transform: rotate(-45deg) translate(4.5px, -4.5px);
}

/* --- Theme Toggle --- */
.theme-toggle {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 32px;
  height: 32px;
  border-radius: 50%;
  color: var(--color-text-muted);
  transition: color var(--transition-fast);
  flex-shrink: 0;
}

.theme-toggle:hover {
  color: var(--color-text);
}

.theme-toggle svg {
  width: 16px;
  height: 16px;
}

.theme-toggle .icon-moon,
[data-theme="dark"] .theme-toggle .icon-sun {
  display: none;
}

[data-theme="dark"] .theme-toggle .icon-moon {
  display: block;
}

[data-theme="dark"] .theme-toggle .icon-sun {
  display: none;
}

/* --- Main Content --- */
.main {
  flex: 1;
  width: 100%;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: calc(var(--nav-height) + var(--spacing-4xl)) var(--spacing-xl) var(--spacing-4xl);
}

/* --- Page Header --- */
.page-header {
  margin-bottom: var(--spacing-3xl);
}

.page-header__label {
  font-size: var(--fs-xs);
  font-weight: var(--fw-medium);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--color-text-muted);
  margin-bottom: var(--spacing-sm);
}

.page-header__title {
  font-size: var(--fs-2xl);
  font-weight: var(--fw-bold);
  letter-spacing: -0.03em;
  line-height: 1.15;
  color: var(--color-text);
}

.page-header__subtitle {
  font-size: var(--fs-md);
  font-weight: var(--fw-normal);
  color: var(--color-text-secondary);
  margin-top: var(--spacing-md);
  line-height: 1.6;
}

/* --- Section --- */
.section {
  margin-bottom: var(--spacing-3xl);
}

.section__title {
  font-size: var(--fs-xs);
  font-weight: var(--fw-medium);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--color-text-muted);
  margin-bottom: var(--spacing-lg);
  padding-bottom: var(--spacing-sm);
  border-bottom: 1px solid var(--color-border);
}

/* --- Card --- */
.card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: var(--spacing-xl);
  transition: border-color var(--transition-base), box-shadow var(--transition-base);
}

.card:hover {
  border-color: var(--color-text-muted);
  box-shadow: 0 2px 12px rgba(0, 0, 0, 0.04);
}

.card__title {
  font-size: var(--fs-base);
  font-weight: var(--fw-semibold);
  color: var(--color-text);
  margin-bottom: var(--spacing-xs);
  letter-spacing: -0.01em;
}

.card__meta {
  font-size: var(--fs-sm);
  color: var(--color-text-muted);
  margin-bottom: var(--spacing-md);
}

.card__description {
  font-size: var(--fs-sm);
  color: var(--color-text-secondary);
  line-height: 1.65;
}

/* --- Tags --- */
.tags {
  display: flex;
  flex-wrap: wrap;
  gap: var(--spacing-sm);
  margin-top: var(--spacing-md);
}

.tag {
  font-size: var(--fs-xs);
  font-weight: var(--fw-medium);
  color: var(--color-tag-text);
  background: var(--color-tag-bg);
  padding: 3px 10px;
  border-radius: 100px;
  letter-spacing: 0.01em;
}

/* --- Timeline --- */
.timeline {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-2xl);
}

.timeline-item {
  position: relative;
  padding-left: var(--spacing-xl);
  border-left: 1.5px solid var(--color-border);
}

.timeline-item::before {
  content: '';
  position: absolute;
  left: -4px;
  top: 6px;
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background: var(--color-text);
}

.timeline-item__header {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  flex-wrap: wrap;
  gap: var(--spacing-sm);
  margin-bottom: var(--spacing-xs);
}

.timeline-item__org {
  font-size: var(--fs-base);
  font-weight: var(--fw-semibold);
  color: var(--color-text);
  letter-spacing: -0.01em;
}

.timeline-item__dates {
  font-size: var(--fs-xs);
  font-weight: var(--fw-normal);
  color: var(--color-text-muted);
  font-family: var(--font-mono);
}

.timeline-item__role {
  font-size: var(--fs-sm);
  color: var(--color-text-secondary);
  margin-bottom: var(--spacing-md);
}

.timeline-item__list {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-sm);
}

.timeline-item__list li {
  font-size: var(--fs-sm);
  color: var(--color-text-secondary);
  line-height: 1.65;
  padding-left: var(--spacing-md);
  position: relative;
}

.timeline-item__list li::before {
  content: '—';
  position: absolute;
  left: 0;
  color: var(--color-text-muted);
  font-size: var(--fs-xs);
}

/* --- Publications List --- */
.pub-list {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-lg);
}

.pub-item {
  padding-bottom: var(--spacing-lg);
  border-bottom: 1px solid var(--color-border-light);
}

.pub-item:last-child {
  border-bottom: none;
  padding-bottom: 0;
}

.pub-item__title {
  font-size: var(--fs-sm);
  font-weight: var(--fw-medium);
  color: var(--color-text);
  line-height: 1.5;
  margin-bottom: var(--spacing-xs);
}

.pub-item__venue {
  font-size: var(--fs-xs);
  color: var(--color-text-muted);
  font-family: var(--font-mono);
}

/* --- Blog Cards --- */
.blog-grid {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-lg);
}

.blog-card {
  padding-bottom: var(--spacing-lg);
  border-bottom: 1px solid var(--color-border-light);
  transition: opacity var(--transition-fast);
}

.blog-card:last-child {
  border-bottom: none;
}

.blog-card:hover {
  opacity: 0.7;
}

.blog-card__date {
  font-size: var(--fs-xs);
  font-family: var(--font-mono);
  color: var(--color-text-muted);
  margin-bottom: var(--spacing-xs);
}

.blog-card__title {
  font-size: var(--fs-md);
  font-weight: var(--fw-semibold);
  color: var(--color-text);
  letter-spacing: -0.01em;
  margin-bottom: var(--spacing-sm);
}

.blog-card__excerpt {
  font-size: var(--fs-sm);
  color: var(--color-text-secondary);
  line-height: 1.65;
}

/* --- Blog Article (Individual Post) --- */
.article-back {
  display: inline-flex;
  align-items: center;
  gap: var(--spacing-xs);
  font-size: var(--fs-sm);
  color: var(--color-text-muted);
  text-decoration: none;
  margin-bottom: var(--spacing-2xl);
  transition: color var(--transition-fast);
}

.article-back:hover {
  color: var(--color-text);
  opacity: 1;
}

.article-meta {
  font-size: var(--fs-xs);
  font-family: var(--font-mono);
  color: var(--color-text-muted);
  margin-bottom: var(--spacing-sm);
}

.article-title {
  font-size: var(--fs-2xl);
  font-weight: var(--fw-bold);
  letter-spacing: -0.03em;
  line-height: 1.2;
  color: var(--color-text);
  margin-bottom: var(--spacing-2xl);
}

.article-body {
  max-width: 100%;
}

.article-body p {
  font-size: var(--fs-base);
  color: var(--color-text-secondary);
  line-height: 1.85;
  margin-bottom: var(--spacing-lg);
}

.article-body h2 {
  font-size: var(--fs-lg);
  font-weight: var(--fw-semibold);
  color: var(--color-text);
  letter-spacing: -0.02em;
  margin-top: var(--spacing-3xl);
  margin-bottom: var(--spacing-md);
}

.article-body h3 {
  font-size: var(--fs-md);
  font-weight: var(--fw-semibold);
  color: var(--color-text);
  margin-top: var(--spacing-2xl);
  margin-bottom: var(--spacing-md);
}

.article-body ul,
.article-body ol {
  margin-bottom: var(--spacing-lg);
  padding-left: var(--spacing-xl);
}

.article-body li {
  font-size: var(--fs-base);
  color: var(--color-text-secondary);
  line-height: 1.85;
  margin-bottom: var(--spacing-sm);
  list-style: disc;
}

.article-body ol li {
  list-style: decimal;
}

.article-body strong {
  color: var(--color-text);
  font-weight: var(--fw-semibold);
}

.article-body code {
  font-family: var(--font-mono);
  font-size: var(--fs-sm);
  background: var(--color-tag-bg);
  color: var(--color-tag-text);
  padding: 2px 6px;
  border-radius: var(--radius-sm);
}

.article-body blockquote {
  border-left: 3px solid var(--color-border);
  padding-left: var(--spacing-lg);
  margin: var(--spacing-xl) 0;
  color: var(--color-text-secondary);
  font-style: italic;
}

/* --- Achievements --- */
.achievement-list {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-md);
}

.achievement-item {
  font-size: var(--fs-sm);
  color: var(--color-text-secondary);
  line-height: 1.65;
  padding-left: var(--spacing-lg);
  position: relative;
}

.achievement-item::before {
  content: '✦';
  position: absolute;
  left: 0;
  color: var(--color-text-muted);
  font-size: var(--fs-xs);
}

/* --- Skills Grid --- */
.skills-grid {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-xl);
}

.skills-group__title {
  font-size: var(--fs-sm);
  font-weight: var(--fw-semibold);
  color: var(--color-text);
  margin-bottom: var(--spacing-sm);
}

.skills-group .tags {
  margin-top: 0;
}

/* --- Contact Form --- */
.contact-form {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-lg);
}

.form-group {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-xs);
}

.form-group label {
  font-size: var(--fs-sm);
  font-weight: var(--fw-medium);
  color: var(--color-text);
}

.form-group input,
.form-group textarea {
  font-family: var(--font-sans);
  font-size: var(--fs-sm);
  color: var(--color-text);
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  padding: var(--spacing-md);
  transition: border-color var(--transition-fast);
  outline: none;
}

.form-group input:focus,
.form-group textarea:focus {
  border-color: var(--color-text);
}

.form-group textarea {
  min-height: 140px;
  resize: vertical;
}

.form-submit {
  align-self: flex-start;
  font-size: var(--fs-sm);
  font-weight: var(--fw-medium);
  color: var(--color-bg);
  background: var(--color-text);
  padding: var(--spacing-md) var(--spacing-2xl);
  border-radius: var(--radius-sm);
  transition: opacity var(--transition-fast);
}

.form-submit:hover {
  opacity: 0.8;
}

/* --- Contact Info --- */
.contact-info {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-sm);
  margin-top: var(--spacing-2xl);
  padding-top: var(--spacing-2xl);
  border-top: 1px solid var(--color-border);
}

.contact-info__item {
  font-size: var(--fs-sm);
  color: var(--color-text-secondary);
}

.contact-info__item a {
  color: var(--color-text);
  text-decoration: underline;
  text-underline-offset: 3px;
  text-decoration-color: var(--color-border);
}

.contact-info__item a:hover {
  text-decoration-color: var(--color-text);
  opacity: 1;
}

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

.footer__inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--spacing-xl);
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.footer__copy {
  font-size: var(--fs-xs);
  color: var(--color-text-muted);
}

.footer__links {
  display: flex;
  gap: var(--spacing-lg);
}

.footer__link {
  font-size: var(--fs-xs);
  color: var(--color-text-muted);
  text-decoration: none;
  transition: color var(--transition-fast);
}

.footer__link:hover {
  color: var(--color-text);
  opacity: 1;
}

/* --- Hero Section --- */
.hero {
  margin-bottom: var(--spacing-2xl);
}

.hero__name {
  font-size: var(--fs-3xl);
  font-weight: var(--fw-bold);
  letter-spacing: -0.04em;
  line-height: 1.1;
  color: var(--color-text);
  margin-bottom: var(--spacing-md);
}

.hero__tagline {
  font-size: var(--fs-md);
  font-weight: var(--fw-normal);
  color: var(--color-text-secondary);
  line-height: 1.6;
  max-width: 560px;
}

.hero__links {
  display: flex;
  align-items: center;
  gap: var(--spacing-sm);
  margin-top: var(--spacing-xl);
  flex-wrap: wrap;
}

.hero__link {
  font-size: var(--fs-sm);
  color: var(--color-text);
  text-decoration: underline;
  text-underline-offset: 3px;
  text-decoration-color: var(--color-border);
}

.hero__link:hover {
  text-decoration-color: var(--color-text);
  opacity: 1;
}

.hero__divider {
  color: var(--color-text-muted);
  font-size: var(--fs-sm);
  user-select: none;
}

.hero__intro {
  margin-bottom: var(--spacing-2xl);
}

.hero__intro p {
  font-size: var(--fs-base);
  color: var(--color-text-secondary);
  line-height: 1.75;
}

.hero__cta {
  display: flex;
  gap: var(--spacing-xl);
}

.hero__cta-link {
  font-size: var(--fs-sm);
  font-weight: var(--fw-medium);
  color: var(--color-text);
  text-decoration: none;
  padding-bottom: 2px;
  border-bottom: 1.5px solid var(--color-text);
  transition: opacity var(--transition-fast);
}

.hero__cta-link:hover {
  opacity: 0.6;
}

/* --- Page Entrance Animation --- */
.fade-in {
  opacity: 0;
  transform: translateY(12px);
  animation: fadeInUp 0.5s ease forwards;
}

.fade-in--delay-1 {
  animation-delay: 0.1s;
}

.fade-in--delay-2 {
  animation-delay: 0.2s;
}

.fade-in--delay-3 {
  animation-delay: 0.3s;
}

.fade-in--delay-4 {
  animation-delay: 0.4s;
}

@keyframes fadeInUp {
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

/* --- Project Cards Grid --- */
.project-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--spacing-lg);
}

/* --- Responsive --- */
@media (max-width: 640px) {
  :root {
    --fs-2xl: 2rem;
    --fs-3xl: 2.5rem;
  }

  .nav__links {
    position: fixed;
    top: 0;
    right: 0;
    bottom: 0;
    width: 260px;
    background: var(--color-bg);
    border-left: 1px solid var(--color-border);
    flex-direction: column;
    padding: calc(var(--nav-height) + var(--spacing-xl)) var(--spacing-xl);
    gap: var(--spacing-md);
    transform: translateX(100%);
    transition: transform var(--transition-base);
  }

  .nav__links.open {
    transform: translateX(0);
  }

  .nav__toggle {
    display: flex;
  }

  .main {
    padding-top: calc(var(--nav-height) + var(--spacing-2xl));
  }

  .timeline-item__header {
    flex-direction: column;
    gap: 2px;
  }

  .footer__inner {
    flex-direction: column;
    gap: var(--spacing-md);
    text-align: center;
  }
}