/* ============================================
   Knucklet — Product Page Styles
   Inherits Unvoiced design language
   ============================================ */

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

:root {
  --bg: #fafaf8;
  --bg-alt: #f3f2ef;
  --text: #1a1a1a;
  --text-muted: #6b6b6b;
  --border: #e0ddd8;
  --accent: #4a4a4a;
  --font-en: 'Playfair Display', Georgia, serif;
  --font-jp: 'Shippori Mincho B1', serif;
  --max-w: 860px;
  --space-xs: 0.5rem;
  --space-sm: 1rem;
  --space-md: 2rem;
  --space-lg: 4rem;
  --space-xl: 6rem;
  --space-2xl: 10rem;
}

html {
  scroll-behavior: smooth;
  font-size: 18px;
}

body {
  font-family: var(--font-jp);
  background: var(--bg);
  color: var(--text);
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

.container {
  max-width: var(--max-w);
  margin: 0 auto;
  padding: 0 var(--space-md);
}

h1, h2, h3 {
  font-family: var(--font-en);
}

/* --- Nav --- */
.nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 100;
  background: rgba(250, 250, 248, 0.9);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
}

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

.nav-left {
  display: flex;
  align-items: center;
  gap: var(--space-md);
}

.nav-logo {
  font-family: var(--font-en);
  font-weight: 600;
  font-size: 1.25rem;
  text-decoration: none;
  color: var(--text);
  letter-spacing: -0.02em;
}

.nav-back {
  font-size: 0.85rem;
  color: var(--text-muted);
  text-decoration: none;
  transition: color 0.2s;
}

.nav-back:hover {
  color: var(--text);
}

/* --- Hero --- */
.hero {
  padding-top: calc(64px + var(--space-2xl));
  padding-bottom: var(--space-xl);
}

.hero-label {
  font-family: var(--font-en);
  font-size: 1rem;
  font-weight: 500;
  color: var(--text-muted);
  letter-spacing: 0.04em;
  margin-bottom: var(--space-sm);
}

.hero-headline {
  font-size: clamp(2.8rem, 7vw, 4.5rem);
  font-weight: 400;
  letter-spacing: -0.03em;
  line-height: 1.1;
  margin-bottom: var(--space-md);
}

.hero-sub {
  font-size: clamp(1rem, 2.5vw, 1.1rem);
  color: var(--text-muted);
  max-width: 560px;
  line-height: 1.8;
  margin-bottom: var(--space-lg);
}

.hero-actions {
  display: flex;
  gap: var(--space-sm);
  flex-wrap: wrap;
}

/* --- Buttons --- */
.btn {
  padding: 0.75rem 1.8rem;
  border-radius: 4px;
  font-size: 0.88rem;
  cursor: pointer;
  transition: opacity 0.2s;
  text-decoration: none;
  display: inline-block;
}

.btn-primary {
  border: 1px solid var(--text);
  background: var(--text);
  color: var(--bg);
}

.btn-secondary {
  border: 1px solid var(--border);
  background: transparent;
  color: var(--text);
}

.btn:hover {
  opacity: 0.75;
}

/* --- Sections (shared) --- */
section {
  padding: var(--space-xl) 0;
}

.section-label {
  font-family: var(--font-jp);
  font-size: 0.8rem;
  color: var(--text-muted);
  letter-spacing: 0.08em;
  margin-bottom: var(--space-xs);
}

.section-headline {
  font-size: clamp(1.8rem, 4vw, 2.5rem);
  font-weight: 400;
  letter-spacing: -0.02em;
  line-height: 1.2;
  margin-bottom: var(--space-lg);
}

.section-border {
  border-top: 1px solid var(--border);
}

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

/* --- Fade-in --- */
.fade-in {
  opacity: 0;
  transform: translateY(24px);
  transition: opacity 0.8s ease, transform 0.8s ease;
}

.fade-in.visible {
  opacity: 1;
  transform: translateY(0);
}

/* --- Overview --- */
.overview-body {
  max-width: 620px;
}

.overview-body p {
  color: var(--text-muted);
  font-size: 1rem;
  margin-bottom: var(--space-sm);
  line-height: 1.8;
}

.overview-body .emphasis {
  color: var(--text);
  font-weight: 500;
}

/* --- How It Works --- */
.steps {
  display: flex;
  flex-direction: column;
  gap: var(--space-lg);
}

.step {
  display: flex;
  gap: var(--space-md);
  align-items: flex-start;
}

.step-num {
  font-family: var(--font-en);
  font-size: 2.5rem;
  font-weight: 400;
  color: var(--border);
  line-height: 1;
  flex-shrink: 0;
  width: 48px;
}

.step-content h3 {
  font-size: 1.15rem;
  font-weight: 500;
  margin-bottom: 4px;
}

.step-content p {
  font-size: 0.95rem;
  color: var(--text-muted);
  line-height: 1.7;
}

/* --- Product images --- */
.product-hero {
  padding: 0 0 var(--space-xl);
}

.product-img {
  width: 100%;
  max-width: 480px;
  margin: 0 auto;
  border-radius: 6px;
  display: block;
}

/* --- Overview split (text + image) --- */
.overview-split {
  display: flex;
  gap: var(--space-lg);
  align-items: center;
}

.overview-split .overview-body {
  flex: 1;
  min-width: 0;
}

.overview-split .section-headline {
  margin-bottom: var(--space-md);
}

.overview-img {
  width: 220px;
  flex-shrink: 0;
  border-radius: 6px;
  display: block;
}

/* --- Footer --- */
.footer {
  padding: var(--space-lg) 0;
  border-top: 1px solid var(--border);
}

.footer-inner {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: var(--space-sm);
}

.footer a {
  color: var(--text-muted);
  text-decoration: none;
  font-size: 0.85rem;
  transition: color 0.2s;
}

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

.footer p {
  font-size: 0.8rem;
  color: var(--text-muted);
}

/* ============================================
   Responsive
   ============================================ */

@media (max-width: 640px) {
  html {
    font-size: 16px;
  }

  .hero {
    padding-top: calc(64px + var(--space-xl));
    padding-bottom: var(--space-xl);
  }

  .hero-actions {
    flex-direction: column;
  }

  .hero-actions .btn {
    text-align: center;
  }

  .step {
    flex-direction: column;
    gap: var(--space-xs);
  }

  .step-num {
    font-size: 2rem;
  }

  .overview-split {
    flex-direction: column;
  }

  .overview-img {
    width: 100%;
    max-width: 360px;
  }

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