/* =========================================================
   Seven Minute Tech — Design System
   ========================================================= */

:root {
  /* Brand */
  --green-500: #73c900;
  --green-600: #5fa800;
  --green-700: #4a8500;
  --green-50:  #f4faea;
  --green-100: #e6f4cf;

  /* Ink */
  --ink-900: #0a0a0a;
  --ink-700: #1f2937;
  --ink-500: #4b5563;
  --ink-400: #6b7280;
  --ink-300: #9ca3af;

  /* Surface */
  --bg:        #ffffff;
  --surface-1: #fafafa;
  --surface-2: #f5f7f2;
  --border:    #e5e7eb;
  --border-2:  #d1d5db;

  /* Accent */
  --gold: #f5b800;

  /* Type scale */
  --fs-12: 0.75rem;
  --fs-14: 0.875rem;
  --fs-16: 1rem;
  --fs-18: 1.125rem;
  --fs-20: 1.25rem;
  --fs-24: 1.5rem;
  --fs-32: 2rem;
  --fs-40: 2.5rem;
  --fs-56: 3.5rem;
  --fs-72: 4.5rem;

  /* Space */
  --s-1: 4px;
  --s-2: 8px;
  --s-3: 12px;
  --s-4: 16px;
  --s-5: 24px;
  --s-6: 32px;
  --s-7: 48px;
  --s-8: 64px;
  --s-9: 96px;
  --s-10: 128px;

  /* Layout */
  --container: 1200px;
  --container-narrow: 880px;

  /* Effects */
  --radius-sm: 6px;
  --radius:    12px;
  --radius-lg: 20px;
  --shadow-1: 0 1px 2px rgba(0,0,0,.04), 0 1px 3px rgba(0,0,0,.06);
  --shadow-2: 0 4px 6px rgba(0,0,0,.04), 0 10px 24px rgba(0,0,0,.08);

  /* Type */
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
  --font-cjk: 'Inter', -apple-system, BlinkMacSystemFont, 'PingFang SC', 'Microsoft YaHei', 'Noto Sans SC', sans-serif;
}

/* =========================================================
   Reset
   ========================================================= */

*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; scroll-behavior: smooth; }
body {
  margin: 0;
  font-family: var(--font-sans);
  font-size: var(--fs-16);
  line-height: 1.6;
  color: var(--ink-700);
  background: var(--bg);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}
html[lang="zh"] body { font-family: var(--font-cjk); }

img, svg { display: block; max-width: 100%; height: auto; }
a { color: inherit; text-decoration: none; }
button { font: inherit; cursor: pointer; }
ul { padding-left: 1.2em; }

h1, h2, h3, h4 {
  font-weight: 800;
  letter-spacing: -0.02em;
  line-height: 1.15;
  color: var(--ink-900);
  margin: 0 0 var(--s-4);
}
h1 { font-size: clamp(2rem, 5vw, var(--fs-56)); letter-spacing: -0.03em; }
h2 { font-size: clamp(1.5rem, 3.5vw, var(--fs-40)); }
h3 { font-size: var(--fs-24); }
h4 { font-size: var(--fs-18); font-weight: 700; }
p  { margin: 0 0 var(--s-4); }

::selection { background: var(--green-500); color: #fff; }

/* =========================================================
   Layout helpers
   ========================================================= */

.container {
  max-width: var(--container);
  margin: 0 auto;
  padding: 0 var(--s-5);
}
.container-narrow {
  max-width: var(--container-narrow);
  margin: 0 auto;
  padding: 0 var(--s-5);
}
.section { padding: var(--s-8) 0; }
.section-lg { padding: var(--s-9) 0; }
@media (min-width: 768px) {
  .section { padding: var(--s-9) 0; }
  .section-lg { padding: var(--s-10) 0; }
}

.eyebrow {
  display: inline-block;
  font-size: var(--fs-12);
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--green-700);
  background: var(--green-50);
  padding: 6px 12px;
  border-radius: 999px;
  margin-bottom: var(--s-4);
}

.lead {
  font-size: var(--fs-20);
  color: var(--ink-500);
  max-width: 60ch;
}

.muted { color: var(--ink-400); }
.hr { height: 1px; background: var(--border); border: 0; margin: var(--s-7) 0; }

/* =========================================================
   Buttons
   ========================================================= */

.btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 14px 22px;
  font-size: var(--fs-16);
  font-weight: 600;
  border-radius: var(--radius);
  border: 2px solid transparent;
  transition: transform .15s ease, background .15s ease, color .15s ease, border-color .15s ease;
  white-space: nowrap;
}
.btn:hover { transform: translateY(-1px); }
.btn-primary {
  background: var(--ink-900);
  color: #fff;
}
.btn-primary:hover { background: var(--green-600); }
.btn-accent {
  background: var(--green-500);
  color: var(--ink-900);
}
.btn-accent:hover { background: var(--green-600); color: #fff; }
.btn-ghost {
  background: transparent;
  color: var(--ink-900);
  border-color: var(--ink-900);
}
.btn-ghost:hover { background: var(--ink-900); color: #fff; }
.btn-sm { padding: 9px 14px; font-size: var(--fs-14); }

.arrow::after { content: "→"; margin-left: 4px; transition: transform .2s ease; }
a:hover .arrow::after, .btn:hover .arrow::after { transform: translateX(3px); }

/* =========================================================
   Header / Nav
   ========================================================= */

.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background: rgba(255,255,255,.92);
  backdrop-filter: saturate(180%) blur(12px);
  -webkit-backdrop-filter: saturate(180%) blur(12px);
  border-bottom: 1px solid var(--border);
}
.nav {
  display: flex;
  align-items: center;
  gap: var(--s-6);
  padding: var(--s-4) 0;
}
.nav-logo img { height: 36px; width: auto; }
.nav-links {
  display: none;
  gap: var(--s-6);
  flex: 1;
  list-style: none;
  margin: 0;
  padding: 0;
}
.nav-links a {
  font-size: var(--fs-14);
  font-weight: 500;
  color: var(--ink-700);
  padding: 8px 0;
  position: relative;
}
.nav-links a:hover { color: var(--ink-900); }
.nav-links a.active::after {
  content: "";
  position: absolute;
  left: 0; right: 0; bottom: -4px;
  height: 3px;
  background: var(--green-500);
  border-radius: 2px;
}
.nav-actions {
  display: flex;
  align-items: center;
  gap: var(--s-4);
  margin-left: auto;
}
.lang-switch {
  display: inline-flex;
  font-size: var(--fs-13, 13px);
  font-weight: 600;
  color: var(--ink-500);
  border: 1px solid var(--border);
  border-radius: 999px;
  overflow: hidden;
}
.lang-switch a {
  padding: 6px 12px;
  color: var(--ink-500);
}
.lang-switch a.active {
  background: var(--ink-900);
  color: #fff;
}
.nav-toggle {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 40px; height: 40px;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  background: #fff;
  color: var(--ink-900);
}
.nav-toggle svg { width: 20px; height: 20px; }

@media (min-width: 960px) {
  .nav-links { display: flex; }
  .nav-toggle { display: none; }
}

/* Mobile menu */
.mobile-menu {
  display: none;
  border-top: 1px solid var(--border);
  background: #fff;
  padding: var(--s-4) 0 var(--s-5);
}
.mobile-menu.open { display: block; }
.mobile-menu ul {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: var(--s-1);
}
.mobile-menu a {
  display: block;
  padding: 12px var(--s-5);
  font-size: var(--fs-16);
  font-weight: 500;
  color: var(--ink-700);
  border-radius: var(--radius-sm);
}
.mobile-menu a:hover { background: var(--surface-2); color: var(--ink-900); }

/* =========================================================
   Hero
   ========================================================= */

.hero {
  position: relative;
  padding: var(--s-8) 0 var(--s-9);
  background:
    radial-gradient(1200px 600px at 90% -10%, var(--green-100), transparent 60%),
    radial-gradient(900px 500px at -10% 30%, #fdf6c2, transparent 55%),
    var(--bg);
  overflow: hidden;
}
@media (min-width: 768px) {
  .hero { padding: var(--s-9) 0 var(--s-10); }
}
.hero h1 {
  font-size: clamp(2.25rem, 6vw, 5rem);
  max-width: 18ch;
  margin-bottom: var(--s-5);
}
.hero h1 em {
  font-style: normal;
  background: linear-gradient(180deg, transparent 65%, var(--green-500) 65%);
  padding: 0 4px;
}
.hero .lead { font-size: clamp(1rem, 1.6vw, 1.25rem); max-width: 58ch; margin-bottom: var(--s-6); }
.hero-cta { display: flex; flex-wrap: wrap; gap: var(--s-3); margin-bottom: var(--s-6); }
.hero-meta {
  display: inline-flex;
  align-items: center;
  gap: var(--s-3);
  font-size: var(--fs-14);
  color: var(--ink-500);
}
.hero-meta .dot {
  width: 8px; height: 8px; border-radius: 50%;
  background: var(--green-500);
  animation: pulse 2s ease-in-out infinite;
}
@keyframes pulse {
  0%, 100% { box-shadow: 0 0 0 0 rgba(115,201,0,.5); }
  50%      { box-shadow: 0 0 0 8px rgba(115,201,0,0); }
}

/* =========================================================
   Page header (inner pages)
   ========================================================= */

.page-header {
  padding: var(--s-7) 0 var(--s-7);
  background: var(--surface-2);
  border-bottom: 1px solid var(--border);
}
.breadcrumb {
  font-size: var(--fs-14);
  color: var(--ink-400);
  margin-bottom: var(--s-3);
}
.breadcrumb a:hover { color: var(--ink-900); }
.breadcrumb .sep { margin: 0 8px; color: var(--ink-300); }
.page-header h1 { margin-bottom: var(--s-3); }
.page-header .lead { font-size: var(--fs-18); }

/* =========================================================
   Pillars / stat row
   ========================================================= */

.pillars {
  display: grid;
  gap: var(--s-5);
  grid-template-columns: 1fr;
}
@media (min-width: 768px) {
  .pillars { grid-template-columns: repeat(3, 1fr); gap: var(--s-6); }
}
.pillar {
  background: var(--surface-2);
  padding: var(--s-6);
  border-radius: var(--radius-lg);
  border: 1px solid var(--border);
}
.pillar .num {
  display: inline-block;
  font-size: var(--fs-14);
  font-weight: 700;
  color: var(--green-700);
  background: var(--green-100);
  padding: 4px 10px;
  border-radius: 999px;
  margin-bottom: var(--s-3);
}
.pillar h3 { font-size: var(--fs-20); }

/* =========================================================
   Steps
   ========================================================= */

.steps {
  display: grid;
  gap: 1px;
  background: var(--border);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  overflow: hidden;
}
.step {
  background: #fff;
  padding: var(--s-5) var(--s-6);
  display: grid;
  grid-template-columns: 64px 1fr;
  gap: var(--s-5);
  align-items: start;
}
.step .step-num {
  font-size: var(--fs-32);
  font-weight: 800;
  color: var(--green-500);
  letter-spacing: -0.04em;
  line-height: 1;
}
.step h3 { font-size: var(--fs-18); margin-bottom: 4px; }
.step p { color: var(--ink-500); margin: 0; }

/* =========================================================
   Cards
   ========================================================= */

.section-head {
  display: flex;
  align-items: flex-end;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: var(--s-4);
  margin-bottom: var(--s-6);
}
.section-head h2 { margin: 0; }
.section-head .lead { margin: 0; }
.section-head .link { font-weight: 600; }

.card-grid {
  display: grid;
  gap: var(--s-5);
  grid-template-columns: 1fr;
}
@media (min-width: 700px) { .card-grid { grid-template-columns: 1fr 1fr; } }
@media (min-width: 1000px) { .card-grid { grid-template-columns: repeat(3, 1fr); } }

.card {
  display: flex;
  flex-direction: column;
  background: #fff;
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  overflow: hidden;
  transition: transform .2s ease, box-shadow .2s ease, border-color .2s ease;
}
.card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow-2);
  border-color: var(--border-2);
}
.card-media {
  aspect-ratio: 16/10;
  background: linear-gradient(135deg, var(--green-100), var(--surface-2));
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--green-700);
  font-weight: 800;
  font-size: var(--fs-32);
  letter-spacing: -0.02em;
  position: relative;
}
.card-media.has-date {
  background: linear-gradient(135deg, #f9fbe0, #ecf6cf);
}
.card-media .date {
  text-align: center;
  line-height: 1.05;
}
.card-media .date .month {
  display: block;
  font-size: var(--fs-14);
  letter-spacing: 0.2em;
  margin-top: var(--s-1);
}
.card-body { padding: var(--s-5) var(--s-6); display: flex; flex-direction: column; gap: 8px; flex: 1; }
.card-body .meta { font-size: var(--fs-13, 13px); color: var(--ink-400); letter-spacing: 0.04em; text-transform: uppercase; }
.card-body h3 { font-size: var(--fs-20); margin: 0; }
.card-body p { color: var(--ink-500); margin: 0; }
.card-body .link {
  margin-top: auto;
  padding-top: var(--s-3);
  font-weight: 600;
  color: var(--ink-900);
}

/* Winner avatar */
.avatar {
  width: 84px; height: 84px;
  border-radius: 50%;
  background: linear-gradient(135deg, var(--green-500), var(--green-700));
  color: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: var(--fs-24);
  letter-spacing: -0.02em;
}
.winner-card { padding: var(--s-6); }
.winner-card .top { display: flex; gap: var(--s-4); align-items: center; margin-bottom: var(--s-4); }
.winner-card h3 { font-size: var(--fs-18); margin: 0 0 2px; }
.winner-card .school { font-size: var(--fs-14); color: var(--ink-500); }
.winner-card .project { font-size: var(--fs-16); color: var(--ink-700); margin: var(--s-2) 0; }

/* Medal badges (replaces emoji for cross-platform compatibility) */
.medal {
  display: inline-block;
  padding: 2px 8px;
  border-radius: 4px;
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.03em;
  white-space: nowrap;
  margin-left: 4px;
}
.medal-gold   { background: #fdf4d4; color: #9c6f00; }
.medal-silver { background: #eef0f3; color: #4b5563; }
.medal-bronze { background: #fcebd9; color: #8b4513; }

/* =========================================================
   Article body
   ========================================================= */

.prose {
  max-width: 72ch;
}
.prose h2 { margin-top: var(--s-8); margin-bottom: var(--s-4); font-size: var(--fs-32); }
.prose h3 { margin-top: var(--s-6); margin-bottom: var(--s-3); font-size: var(--fs-20); }
.prose p, .prose li { color: var(--ink-700); }
.prose ul, .prose ol { padding-left: 1.4em; }
.prose li { margin-bottom: var(--s-2); }
.prose strong { color: var(--ink-900); }
.prose a { color: var(--green-700); text-decoration: underline; text-underline-offset: 3px; }
.prose a:hover { color: var(--green-600); }
.prose blockquote {
  border-left: 4px solid var(--green-500);
  padding: 4px 0 4px var(--s-4);
  margin: var(--s-5) 0;
  font-size: var(--fs-18);
  color: var(--ink-700);
}

.callout {
  background: var(--green-50);
  border: 1px solid var(--green-100);
  border-radius: var(--radius);
  padding: var(--s-5) var(--s-6);
  margin: var(--s-5) 0;
}
.callout h4 { color: var(--green-700); margin-bottom: var(--s-2); }
.callout p:last-child { margin-bottom: 0; }

/* Article + sidebar layout */
.article-grid {
  display: grid;
  gap: var(--s-7);
  grid-template-columns: 1fr;
}
@media (min-width: 1000px) {
  .article-grid { grid-template-columns: minmax(0,1fr) 280px; gap: var(--s-8); }
}
.sidebar {
  position: sticky;
  top: 96px;
  align-self: start;
}
.sidebar h4 {
  font-size: var(--fs-12);
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--ink-400);
  margin-bottom: var(--s-3);
}
.sidebar ul { list-style: none; padding: 0; margin: 0 0 var(--s-5); }
.sidebar li { margin-bottom: var(--s-2); }
.sidebar a {
  display: block;
  padding: 8px 12px;
  border-left: 2px solid var(--border);
  font-size: var(--fs-14);
  color: var(--ink-500);
}
.sidebar a:hover, .sidebar a.active {
  color: var(--ink-900);
  border-left-color: var(--green-500);
  background: var(--surface-2);
}

/* =========================================================
   Tables
   ========================================================= */

.table {
  width: 100%;
  border-collapse: collapse;
  font-size: var(--fs-15, 15px);
}
.table th, .table td {
  text-align: left;
  padding: var(--s-3) var(--s-4);
  border-bottom: 1px solid var(--border);
}
.table th {
  font-weight: 700;
  color: var(--ink-900);
  background: var(--surface-2);
  font-size: var(--fs-13, 13px);
  letter-spacing: 0.05em;
  text-transform: uppercase;
}

/* =========================================================
   Newsletter
   ========================================================= */

.newsletter {
  background: var(--ink-900);
  color: #fff;
  border-radius: var(--radius-lg);
  padding: var(--s-7) var(--s-6);
}
@media (min-width: 768px) {
  .newsletter { padding: var(--s-8); }
}
.newsletter-grid {
  display: grid;
  gap: var(--s-5);
  align-items: center;
}
@media (min-width: 800px) {
  .newsletter-grid { grid-template-columns: 1fr 1fr; gap: var(--s-7); }
}
.newsletter h2 { color: #fff; margin: 0 0 var(--s-3); }
.newsletter p { color: rgba(255,255,255,.7); margin: 0; }
.newsletter form {
  display: flex;
  flex-wrap: wrap;
  gap: var(--s-2);
}
.newsletter input {
  flex: 1;
  min-width: 200px;
  padding: 14px 16px;
  font-size: var(--fs-16);
  border: 0;
  border-radius: var(--radius);
  background: rgba(255,255,255,.1);
  color: #fff;
}
.newsletter input::placeholder { color: rgba(255,255,255,.5); }
.newsletter input:focus { outline: 2px solid var(--green-500); background: rgba(255,255,255,.15); }
.newsletter button {
  padding: 14px 22px;
  background: var(--green-500);
  color: var(--ink-900);
  font-weight: 700;
  border: 0;
  border-radius: var(--radius);
}
.newsletter button:hover { background: #fff; }

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

.site-footer {
  background: var(--ink-900);
  color: rgba(255,255,255,.7);
  padding: var(--s-8) 0 var(--s-5);
  margin-top: var(--s-9);
}
.footer-grid {
  display: grid;
  gap: var(--s-6);
  grid-template-columns: 1fr;
  margin-bottom: var(--s-7);
}
@media (min-width: 700px) {
  .footer-grid { grid-template-columns: 2fr 1fr 1fr 1fr; }
}
.footer-brand img { height: 32px; filter: brightness(0) invert(1); margin-bottom: var(--s-3); }
.footer-brand p { font-size: var(--fs-14); max-width: 30ch; }
.footer-col h4 {
  color: #fff;
  font-size: var(--fs-12);
  letter-spacing: 0.12em;
  text-transform: uppercase;
  margin-bottom: var(--s-4);
}
.footer-col ul { list-style: none; padding: 0; margin: 0; }
.footer-col li { margin-bottom: var(--s-2); }
.footer-col a { font-size: var(--fs-14); color: rgba(255,255,255,.7); }
.footer-col a:hover { color: var(--green-500); }
.footer-bottom {
  padding-top: var(--s-5);
  border-top: 1px solid rgba(255,255,255,.1);
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: var(--s-3);
  font-size: var(--fs-13, 13px);
}
.footer-bottom .legal { display: flex; gap: var(--s-4); flex-wrap: wrap; }
.footer-bottom a:hover { color: var(--green-500); }

/* =========================================================
   Forms (contact)
   ========================================================= */

.form-grid {
  display: grid;
  gap: var(--s-4);
}
.form-row {
  display: grid;
  gap: var(--s-4);
  grid-template-columns: 1fr;
}
@media (min-width: 600px) { .form-row { grid-template-columns: 1fr 1fr; } }
.form-field { display: flex; flex-direction: column; gap: 6px; }
.form-field label { font-size: var(--fs-14); font-weight: 600; color: var(--ink-700); }
.form-field input, .form-field textarea, .form-field select {
  font: inherit;
  padding: 12px 14px;
  border: 1px solid var(--border-2);
  border-radius: var(--radius-sm);
  background: #fff;
  color: var(--ink-700);
}
.form-field input:focus, .form-field textarea:focus, .form-field select:focus {
  outline: 2px solid var(--green-500);
  outline-offset: -1px;
  border-color: var(--green-500);
}
.form-field textarea { min-height: 140px; resize: vertical; }

/* =========================================================
   Utilities
   ========================================================= */

.text-center { text-align: center; }
.mt-0 { margin-top: 0 !important; }
.mt-4 { margin-top: var(--s-4); }
.mt-6 { margin-top: var(--s-6); }
.mt-8 { margin-top: var(--s-8); }
.mb-0 { margin-bottom: 0 !important; }
.flex { display: flex; }
.flex-gap { display: flex; gap: var(--s-3); flex-wrap: wrap; }
.bg-surface { background: var(--surface-2); }

.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;
}