/*
Theme Name: Yunan Song Portfolio
Theme URI: https://www.yunansong.com
Author: Yunan Song
Author URI: https://www.yunansong.com
Description: Personal portfolio theme for Yunan Song, a mechanical engineer. Migrated from Wix.
Version: 1.0.0
License: GNU General Public License v2 or later
License URI: http://www.gnu.org/licenses/gpl-2.0.html
Text Domain: yunan-song
Tags: portfolio, one-page, responsive
*/

/* =============================================
   CSS RESET & BASE
   ============================================= */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  --color-bg: #ffffff;
  --color-surface: #f7f7f7;
  --color-text: #1a1a1a;
  --color-text-muted: #666666;
  --color-accent: #1c3d5a;
  --color-accent-light: #2d6a9f;
  --color-border: #e0e0e0;
  --color-footer-bg: #1a1a1a;
  --color-footer-text: #cccccc;

  --font-heading: 'DM Serif Display', Georgia, serif;
  --font-body: 'Inter', 'Helvetica Neue', sans-serif;
  --font-mono: 'JetBrains Mono', 'Courier New', monospace;

  --max-width: 1100px;
  --section-padding: 80px 24px;
  --radius: 4px;
  --transition: 0.25s ease;
}

html {
  scroll-behavior: smooth;
  font-size: 16px;
}

body {
  font-family: var(--font-body);
  background-color: var(--color-bg);
  color: var(--color-text);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

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

a:hover {
  opacity: 0.75;
  text-decoration: underline;
}

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

ul {
  list-style: none;
}

/* =============================================
   TYPOGRAPHY
   ============================================= */
h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-heading);
  line-height: 1.2;
  color: var(--color-text);
}

h1 { font-size: clamp(2.4rem, 5vw, 4rem); }
h2 { font-size: clamp(1.6rem, 3vw, 2.4rem); }
h3 { font-size: 1.25rem; }

p {
  margin-bottom: 1em;
}

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

/* =============================================
   LAYOUT HELPERS
   ============================================= */
.container {
  max-width: var(--max-width);
  margin-left: auto;
  margin-right: auto;
  padding-left: 24px;
  padding-right: 24px;
}

.section {
  padding: var(--section-padding);
}

.section--alt {
  background-color: var(--color-surface);
}

.section-title {
  font-size: clamp(0.65rem, 1.5vw, 0.75rem);
  font-family: var(--font-body);
  font-weight: 700;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--color-accent);
  margin-bottom: 48px;
  display: flex;
  align-items: center;
  gap: 16px;
}

.section-title::after {
  content: '';
  flex: 1;
  height: 1px;
  background: var(--color-border);
}

/* =============================================
   HEADER / NAV
   ============================================= */
#site-header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 1000;
  background: rgba(255, 255, 255, 0.95);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--color-border);
  transition: box-shadow var(--transition);
}

#site-header.scrolled {
  box-shadow: 0 2px 20px rgba(0,0,0,0.08);
}

.header-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 24px;
  height: 64px;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.site-logo {
  font-family: var(--font-heading);
  font-size: 1.2rem;
  color: var(--color-text);
  font-weight: 400;
  letter-spacing: 0.02em;
}

.site-logo:hover {
  opacity: 1;
  text-decoration: none;
}

.site-nav {
  display: flex;
  align-items: center;
  gap: 36px;
}

.site-nav a {
  font-size: 0.75rem;
  font-weight: 600;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--color-text-muted);
  text-decoration: none;
  transition: color var(--transition);
}

.site-nav a:hover {
  color: var(--color-accent);
  opacity: 1;
  text-decoration: none;
}

/* Mobile menu toggle */
.nav-toggle {
  display: none;
  flex-direction: column;
  gap: 5px;
  cursor: pointer;
  background: none;
  border: none;
  padding: 4px;
}

.nav-toggle span {
  display: block;
  width: 22px;
  height: 2px;
  background: var(--color-text);
  transition: var(--transition);
}

/* =============================================
   HERO SECTION
   ============================================= */
#hero {
  min-height: 100vh;
  display: flex;
  align-items: center;
  padding-top: 64px;
  background: linear-gradient(135deg, #f8f9fb 0%, #ffffff 60%, #eef3f8 100%);
  position: relative;
  overflow: hidden;
}

#hero::before {
  content: '';
  position: absolute;
  top: -200px;
  right: -200px;
  width: 600px;
  height: 600px;
  border-radius: 50%;
  background: radial-gradient(circle, rgba(28,61,90,0.04) 0%, transparent 70%);
  pointer-events: none;
}

.hero-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 24px;
  display: grid;
  grid-template-columns: 1fr 340px;
  gap: 64px;
  align-items: center;
  width: 100%;
}

.hero-eyebrow {
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--color-accent-light);
  margin-bottom: 20px;
}

.hero-name {
  font-size: clamp(2.8rem, 6vw, 5rem);
  font-weight: 400;
  margin-bottom: 8px;
  line-height: 1.05;
}

.hero-name .chinese {
  font-size: 0.45em;
  color: var(--color-text-muted);
  display: block;
  margin-top: 6px;
  letter-spacing: 0.05em;
}

.hero-tagline {
  font-size: 1.05rem;
  color: var(--color-text-muted);
  margin-top: 20px;
  margin-bottom: 32px;
  max-width: 480px;
  line-height: 1.7;
}

.hero-cta {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  background: var(--color-accent);
  color: #fff;
  padding: 12px 28px;
  border-radius: var(--radius);
  font-size: 0.8rem;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  transition: background var(--transition), transform var(--transition);
  text-decoration: none;
}

.hero-cta:hover {
  background: var(--color-accent-light);
  transform: translateY(-1px);
  opacity: 1;
  text-decoration: none;
  color: #fff;
}

.hero-photo {
  width: 280px;
  height: 280px;
  border-radius: 50%;
  object-fit: cover;
  border: 6px solid #fff;
  box-shadow: 0 20px 60px rgba(0,0,0,0.12), 0 4px 16px rgba(0,0,0,0.08);
  justify-self: center;
}

/* =============================================
   EXPERIENCE SECTION
   ============================================= */
#experience {
  padding: var(--section-padding);
}

.experience-list {
  display: flex;
  flex-direction: column;
  gap: 0;
}

.experience-item {
  display: grid;
  grid-template-columns: 200px 1fr;
  gap: 32px;
  padding: 40px 0;
  border-bottom: 1px solid var(--color-border);
}

.experience-item:first-child {
  padding-top: 0;
}

.experience-item:last-child {
  border-bottom: none;
}

.exp-meta {
  padding-top: 4px;
}

.exp-date {
  font-size: 0.78rem;
  font-weight: 600;
  color: var(--color-accent);
  letter-spacing: 0.04em;
  margin-bottom: 4px;
}

.exp-location {
  font-size: 0.78rem;
  color: var(--color-text-muted);
}

.exp-content {}

.exp-company {
  font-size: 1.1rem;
  font-family: var(--font-heading);
  font-weight: 400;
  color: var(--color-text);
  margin-bottom: 2px;
}

.exp-title {
  font-size: 0.82rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--color-accent-light);
  margin-bottom: 12px;
}

.exp-desc {
  font-size: 0.92rem;
  color: var(--color-text-muted);
  line-height: 1.7;
  margin-bottom: 10px;
}

.exp-links {
  margin-top: 12px;
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.exp-link {
  font-size: 0.76rem;
  font-weight: 600;
  color: var(--color-accent-light);
  border: 1px solid var(--color-accent-light);
  padding: 4px 10px;
  border-radius: 20px;
  text-decoration: none;
  transition: all var(--transition);
}

.exp-link:hover {
  background: var(--color-accent-light);
  color: #fff;
  opacity: 1;
  text-decoration: none;
}

/* =============================================
   EDUCATION SECTION
   ============================================= */
#education {
  padding: var(--section-padding);
}

.education-list {
  display: flex;
  flex-direction: column;
  gap: 32px;
}

.education-item {
  display: grid;
  grid-template-columns: 200px 1fr;
  gap: 32px;
  padding-bottom: 32px;
  border-bottom: 1px solid var(--color-border);
}

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

.edu-year {
  font-size: 0.78rem;
  font-weight: 700;
  color: var(--color-accent);
  letter-spacing: 0.04em;
  padding-top: 4px;
}

.edu-school {
  font-size: 1.05rem;
  font-family: var(--font-heading);
  margin-bottom: 4px;
}

.edu-degree {
  font-size: 0.88rem;
  color: var(--color-text-muted);
  margin-bottom: 4px;
}

.edu-location {
  font-size: 0.78rem;
  color: var(--color-text-muted);
}

/* =============================================
   SKILLS SECTION
   ============================================= */
#skills {
  padding: var(--section-padding);
}

.skills-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 24px;
}

.skill-card {
  background: #fff;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 24px;
  transition: box-shadow var(--transition), transform var(--transition);
}

.skill-card:hover {
  box-shadow: 0 8px 30px rgba(0,0,0,0.08);
  transform: translateY(-2px);
}

.skill-category {
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--color-accent);
  margin-bottom: 12px;
}

.skill-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}

.skill-tag {
  font-size: 0.78rem;
  background: var(--color-surface);
  color: var(--color-text);
  padding: 4px 10px;
  border-radius: 3px;
}

/* =============================================
   CONTACT SECTION
   ============================================= */
#contact {
  padding: var(--section-padding);
  text-align: center;
}

.contact-inner {
  max-width: 560px;
  margin: 0 auto;
}

.contact-headline {
  font-size: clamp(1.8rem, 4vw, 3rem);
  margin-bottom: 16px;
}

.contact-sub {
  font-size: 1rem;
  color: var(--color-text-muted);
  margin-bottom: 36px;
}

.contact-btn {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  background: var(--color-accent);
  color: #fff;
  padding: 14px 32px;
  border-radius: var(--radius);
  font-weight: 600;
  font-size: 0.85rem;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  text-decoration: none;
  transition: background var(--transition), transform var(--transition);
}

.contact-btn:hover {
  background: var(--color-accent-light);
  transform: translateY(-1px);
  color: #fff;
  opacity: 1;
  text-decoration: none;
}

/* =============================================
   FOOTER
   ============================================= */
#site-footer {
  background: var(--color-footer-bg);
  color: var(--color-footer-text);
  padding: 40px 24px;
  text-align: center;
}

.footer-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 16px;
}

.footer-copy {
  font-size: 0.8rem;
  color: #777;
}

.footer-social {
  display: flex;
  gap: 20px;
}

.footer-social a {
  font-size: 0.78rem;
  font-weight: 600;
  color: #888;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  text-decoration: none;
  transition: color var(--transition);
}

.footer-social a:hover {
  color: #fff;
  opacity: 1;
}

/* =============================================
   RESPONSIVE
   ============================================= */
@media (max-width: 860px) {
  .hero-inner {
    grid-template-columns: 1fr;
    text-align: center;
    gap: 40px;
  }

  .hero-photo {
    width: 200px;
    height: 200px;
    order: -1;
  }

  .hero-tagline {
    margin-left: auto;
    margin-right: auto;
  }

  .experience-item,
  .education-item {
    grid-template-columns: 1fr;
    gap: 8px;
  }

  .site-nav {
    display: none;
    position: fixed;
    top: 64px;
    left: 0;
    right: 0;
    background: #fff;
    flex-direction: column;
    padding: 24px;
    gap: 20px;
    border-bottom: 1px solid var(--color-border);
    box-shadow: 0 8px 24px rgba(0,0,0,0.1);
  }

  .site-nav.open {
    display: flex;
  }

  .nav-toggle {
    display: flex;
  }

  .skills-grid {
    grid-template-columns: 1fr 1fr;
  }

  .footer-inner {
    flex-direction: column;
    text-align: center;
  }
}

@media (max-width: 480px) {
  :root {
    --section-padding: 56px 20px;
  }

  .skills-grid {
    grid-template-columns: 1fr;
  }
}