/* ============================================================
   main.css — Production Stylesheet
   Machine Design AI Assistant
   ============================================================ */

:root {
  --color-bg: #0f172a; --color-bg-card: #1e293b; --color-bg-input: #1e293b;
  --color-surface: #334155; --color-primary: #6366f1; --color-primary-hov: #4f46e5;
  --color-accent: #06b6d4; --color-text: #f1f5f9; --color-text-muted: #94a3b8;
  --color-border: #334155; --color-error: #f87171; --color-success: #4ade80;
  --font-sans: 'Segoe UI', system-ui, -apple-system, sans-serif;
  --font-mono: 'Cascadia Code', 'Fira Code', monospace;
  --text-xs: 0.75rem; --text-sm: 0.875rem; --text-base: 1rem;
  --text-lg: 1.125rem; --text-xl: 1.25rem; --text-2xl: 1.5rem;
  --text-3xl: 1.875rem; --text-4xl: 2.25rem; --text-5xl: 3rem; --text-6xl: 3.75rem;
  --fw-normal: 400; --fw-medium: 500; --fw-semibold: 600; --fw-bold: 700;
  --lh-tight: 1.25; --lh-normal: 1.5; --lh-relaxed: 1.75;
  --space-1: 0.25rem; --space-2: 0.5rem; --space-3: 0.75rem; --space-4: 1rem;
  --space-5: 1.25rem; --space-6: 1.5rem; --space-8: 2rem; --space-10: 2.5rem;
  --space-12: 3rem; --space-16: 4rem; --space-20: 5rem; --space-24: 6rem;
  --max-w-content: 1200px; --max-w-narrow: 720px;
  --radius-sm: 0.375rem; --radius-md: 0.75rem; --radius-lg: 1rem;
  --radius-xl: 1.5rem; --radius-full: 9999px;
  --shadow-sm: 0 1px 3px rgba(0,0,0,.4); --shadow-md: 0 4px 16px rgba(0,0,0,.4);
  --shadow-lg: 0 10px 40px rgba(0,0,0,.5);
  --transition: 200ms ease; --transition-slow: 400ms ease;
}

*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }
body {
  font-family: var(--font-sans); font-size: var(--text-base);
  line-height: var(--lh-normal); color: var(--color-text);
  background-color: var(--color-bg); min-height: 100vh;
  display: flex; flex-direction: column;
}
main { flex: 1; }
img, video, svg { display: block; max-width: 100%; }
a { color: var(--color-primary); text-decoration: none; transition: color var(--transition); }
a:hover { color: var(--color-primary-hov); }
h1,h2,h3,h4,h5,h6 { line-height: var(--lh-tight); font-weight: var(--fw-bold); }
p { color: var(--color-text-muted); line-height: var(--lh-relaxed); }
ul { list-style: none; }
button { cursor: pointer; border: none; background: none; font: inherit; }

.container { width: 100%; max-width: var(--max-w-content); margin-inline: auto; padding-inline: var(--space-6); }
.section { padding-block: var(--space-24); }
.text-gradient {
  background: linear-gradient(135deg, var(--color-primary), var(--color-accent));
  -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text;
}
.skip-link {
  position: absolute; top: -100%; left: var(--space-4); z-index: 9999;
  padding: var(--space-2) var(--space-4); background: var(--color-primary); color: #fff;
  border-radius: var(--radius-sm); font-weight: var(--fw-semibold); transition: top var(--transition);
}
.skip-link:focus { top: var(--space-4); }
.badge {
  display: inline-block; padding: var(--space-1) var(--space-4);
  background: rgba(99,102,241,.2); border: 1px solid rgba(99,102,241,.4);
  border-radius: var(--radius-full); font-size: var(--text-sm);
  font-weight: var(--fw-medium); color: var(--color-primary); margin-bottom: var(--space-4);
}

.btn {
  display: inline-flex; align-items: center; justify-content: center;
  gap: var(--space-2); padding: var(--space-3) var(--space-6);
  border-radius: var(--radius-md); font-size: var(--text-base);
  font-weight: var(--fw-semibold);
  transition: background var(--transition), transform var(--transition), box-shadow var(--transition);
  white-space: nowrap;
}
.btn:focus-visible { outline: 2px solid var(--color-primary); outline-offset: 3px; }
.btn--primary { background: var(--color-primary); color: #fff; box-shadow: 0 0 20px rgba(99,102,241,.35); }
.btn--primary:hover { background: var(--color-primary-hov); transform: translateY(-2px); box-shadow: 0 0 30px rgba(99,102,241,.5); color: #fff; }
.btn--outline { background: transparent; color: var(--color-text); border: 1.5px solid var(--color-border); }
.btn--outline:hover { border-color: var(--color-primary); color: var(--color-primary); transform: translateY(-2px); }
.btn--full { width: 100%; }

.site-header {
  position: sticky; top: 0; z-index: 100;
  background: rgba(15,23,42,.85);
  backdrop-filter: blur(12px); -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--color-border);
.hero {
  padding-block: var(--space-24);
  background: radial-gradient(ellipse 80% 60% at 50% -10%, rgba(99,102,241,.2) 0%, transparent 70%);
}
.hero__inner { display: grid; grid-template-columns: 1fr 1fr; gap: var(--space-12); align-items: center; }
.hero__title { font-size: clamp(var(--text-4xl), 5vw, var(--text-6xl)); margin-block: var(--space-4) var(--space-6); }
.hero__subtitle { font-size: var(--text-lg); color: var(--color-text-muted); margin-bottom: var(--space-8); max-width: 46ch; }
.hero__actions { display: flex; gap: var(--space-4); flex-wrap: wrap; }
.hero__visual { display: flex; align-items: center; justify-content: center; }
.hero__card {
  background: var(--color-bg-card); border: 1px solid var(--color-border);
  border-radius: var(--radius-xl); padding: var(--space-12);
  text-align: center; box-shadow: var(--shadow-lg);
  animation: float 4s ease-in-out infinite;
}
.hero__card-icon { font-size: 4rem; }
.hero__card-label { margin-top: var(--space-4); font-weight: var(--fw-semibold); color: var(--color-text); }
@keyframes float { 0%, 100% { transform: translateY(0); } 50% { transform: translateY(-12px); } }

.section__title { font-size: clamp(var(--text-3xl), 4vw, var(--text-4xl)); margin-bottom: var(--space-4); }
.section__subtitle { font-size: var(--text-lg); color: var(--color-text-muted); margin-bottom: var(--space-12); }

.features { background: var(--color-bg); }
.features .section__title, .features .section__subtitle { text-align: center; }
.features__grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(280px, 1fr)); gap: var(--space-6); }
.feature-card {
  background: var(--color-bg-card); border: 1px solid var(--color-border);
  border-radius: var(--radius-lg); padding: var(--space-8);
  transition: transform var(--transition), box-shadow var(--transition), border-color var(--transition);
}
.feature-card:hover { transform: translateY(-4px); box-shadow: var(--shadow-lg); border-color: var(--color-primary); }
.feature-card__icon { font-size: 2rem; margin-bottom: var(--space-4); }
.feature-card__title { font-size: var(--text-lg); margin-bottom: var(--space-2); color: var(--color-text); }
.feature-card__desc { font-size: var(--text-sm); color: var(--color-text-muted); }

.about {
  background: linear-gradient(135deg, rgba(99,102,241,.07), rgba(6,182,212,.07));
  border-top: 1px solid var(--color-border); border-bottom: 1px solid var(--color-border);
}
.about__inner { display: grid; grid-template-columns: 1fr 1fr; gap: var(--space-16); align-items: center; }
.about__list { margin-top: var(--space-6); display: flex; flex-direction: column; gap: var(--space-3); }
.about__list li { color: var(--color-text); font-weight: var(--fw-medium); }
.about__stats { display: grid; grid-template-columns: 1fr 1fr; gap: var(--space-6); }
.stat { background: var(--color-bg-card); border: 1px solid var(--color-border); border-radius: var(--radius-lg); padding: var(--space-8); text-align: center; }
.stat:first-child { grid-column: span 2; }
.stat__num {
  display: block; font-size: var(--text-5xl); font-weight: var(--fw-bold);
  background: linear-gradient(135deg, var(--color-primary), var(--color-accent));
  -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text;
}
.stat__label { font-size: var(--text-sm); color: var(--color-text-muted); margin-top: var(--space-2); }

.contact { background: var(--color-bg); }
.contact .section__title { text-align: center; margin-bottom: var(--space-10); }
.contact__form { max-width: var(--max-w-narrow); margin-inline: auto; display: flex; flex-direction: column; gap: var(--space-5); }
.form-group { display: flex; flex-direction: column; gap: var(--space-2); }
.form-label { font-size: var(--text-sm); font-weight: var(--fw-semibold); color: var(--color-text); }
.form-input {
  background: var(--color-bg-input); border: 1.5px solid var(--color-border);
  border-radius: var(--radius-md); padding: var(--space-3) var(--space-4);
  font-size: var(--text-base); font-family: var(--font-sans); color: var(--color-text);
  transition: border-color var(--transition), box-shadow var(--transition); width: 100%;
}
.form-input::placeholder { color: var(--color-surface); }
.form-input:focus { outline: none; border-color: var(--color-primary); box-shadow: 0 0 0 3px rgba(99,102,241,.25); }
.form-input.is-invalid { border-color: var(--color-error); }
.form-textarea { resize: vertical; min-height: 130px; }
.form-error { font-size: var(--text-sm); color: var(--color-error); min-height: 1.2em; }
.form-success { text-align: center; color: var(--color-success); font-weight: var(--fw-semibold); padding: var(--space-4); }

.site-footer { background: var(--color-bg-card); border-top: 1px solid var(--color-border); padding-block: var(--space-8); }
.footer__inner { display: flex; align-items: center; justify-content: space-between; gap: var(--space-4); flex-wrap: wrap; }
.footer__copy { font-size: var(--text-sm); color: var(--color-text-muted); }
.footer__links { display: flex; gap: var(--space-6); }
.footer__links a { font-size: var(--text-sm); color: var(--color-text-muted); transition: color var(--transition); }
.footer__links a:hover { color: var(--color-text); }

@media (max-width: 768px) {
  .nav__toggle { display: flex; align-items: center; justify-content: center; width: 2.5rem; height: 2.5rem; border-radius: var(--radius-sm); border: 1.5px solid var(--color-border); }
  .hamburger, .hamburger::before, .hamburger::after { display: block; width: 1.2rem; height: 2px; background: var(--color-text); transition: transform var(--transition); position: relative; }
  .hamburger::before, .hamburger::after { content: ''; position: absolute; left: 0; }
  .hamburger::before { top: -6px; }
  .hamburger::after  { top:  6px; }
  .nav__menu { display: none; position: absolute; top: 4.5rem; left: 0; right: 0; background: var(--color-bg-card); border-bottom: 1px solid var(--color-border); flex-direction: column; align-items: flex-start; padding: var(--space-4) var(--space-6); gap: var(--space-4); }
  .nav__menu.is-open { display: flex; }
  .hero__inner { grid-template-columns: 1fr; }
  .hero__visual { display: none; }
  .about__inner { grid-template-columns: 1fr; }
  .about__stats { grid-template-columns: 1fr 1fr; }
  .stat:first-child { grid-column: auto; }
  .footer__inner { flex-direction: column; text-align: center; }
}
@media (max-width: 480px) {
  .hero__actions { flex-direction: column; }
  .btn { width: 100%; justify-content: center; }
  .about__stats { grid-template-columns: 1fr; }
}
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation-duration: .01ms !important; transition-duration: .01ms !important; }
  html { scroll-behavior: auto; }
}
:focus-visible { outline: 2px solid var(--color-primary); outline-offset: 3px; border-radius: var(--radius-sm); }
}
.nav { display: flex; align-items: center; justify-content: space-between; height: 4.5rem; }
.nav__logo-text {
  font-size: var(--text-xl); font-weight: var(--fw-bold);
  background: linear-gradient(135deg, var(--color-primary), var(--color-accent));
  -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text;
}
.nav__menu { display: flex; align-items: center; gap: var(--space-6); }
.nav__link { color: var(--color-text-muted); font-weight: var(--fw-medium); font-size: var(--text-sm); transition: color var(--transition); }
.nav__link:hover { color: var(--color-text); }
.nav__link--cta { padding: var(--space-2) var(--space-4); background: var(--color-primary); color: #fff !important; border-radius: var(--radius-md); font-size: var(--text-sm); }
.nav__link--cta:hover { background: var(--color-primary-hov); }
.nav__toggle { display: none; }