:root {
  --color-bg: #ffffff;
  --color-bg-alt: #f7f7f5;
  --color-fg: #1a1a1a;
  --color-fg-muted: #5a5a5a;
  --color-border: #e6e6e2;
  --color-accent: #111111;
  --color-link: #1a1a1a;
  --color-error: #b00020;
  --color-success: #1e6f3a;
  --max-w: 880px;
  --radius: 6px;
  --font-sans:
    -apple-system, BlinkMacSystemFont, "Helvetica Neue", "Hiragino Sans",
    "Hiragino Kaku Gothic ProN", "Noto Sans JP", Meiryo, sans-serif;
}

* {
  box-sizing: border-box;
}

html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }
}

/* sticky ヘッダーの高さ分、アンカー移動先をずらす */
section[id] {
  scroll-margin-top: 64px;
}

body {
  margin: 0;
  background: var(--color-bg);
  color: var(--color-fg);
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.8;
  letter-spacing: 0.02em;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

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

a {
  color: var(--color-link);
  text-decoration: underline;
  text-underline-offset: 3px;
  text-decoration-thickness: 1px;
}

a:hover {
  text-decoration-thickness: 2px;
}

.container {
  width: 100%;
  max-width: var(--max-w);
  margin: 0 auto;
  padding: 0 24px;
}

/* Skip link */
.skip-link {
  position: absolute;
  left: -9999px;
  top: 0;
  z-index: 100;
  padding: 12px 20px;
  background: var(--color-accent);
  color: #fff;
  text-decoration: none;
  border-radius: 0 0 var(--radius) 0;
}

.skip-link:focus {
  left: 0;
}

/* Header */
.site-header {
  position: sticky;
  top: 0;
  z-index: 10;
  background: rgba(255, 255, 255, 0.92);
  backdrop-filter: saturate(180%) blur(8px);
  border-bottom: 1px solid var(--color-border);
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 64px;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  font-weight: 600;
  text-decoration: none;
  color: var(--color-fg);
}

.brand-mark {
  display: inline-grid;
  place-items: center;
  width: 32px;
  height: 32px;
  background: var(--color-accent);
  color: #fff;
  border-radius: var(--radius);
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0.05em;
}

.brand-name {
  font-size: 15px;
  letter-spacing: 0.04em;
}

.site-nav {
  display: flex;
  gap: 24px;
}

.site-nav a {
  font-size: 14px;
  color: var(--color-fg-muted);
  text-decoration: none;
}

.site-nav a:hover {
  color: var(--color-fg);
}

/* Hero */
.hero {
  padding: 120px 0 96px;
  border-bottom: 1px solid var(--color-border);
}

.hero-eyebrow {
  margin: 0 0 16px;
  font-size: 12px;
  letter-spacing: 0.3em;
  color: var(--color-fg-muted);
  text-transform: uppercase;
}

.hero-title {
  margin: 0 0 24px;
  font-size: clamp(32px, 6vw, 56px);
  line-height: 1.25;
  letter-spacing: 0.02em;
  font-weight: 700;
}

.hero-lead {
  margin: 0;
  max-width: 640px;
  font-size: 17px;
  color: var(--color-fg-muted);
}

/* Sections */
.section {
  padding: 96px 0;
}

.section-alt {
  background: var(--color-bg-alt);
  border-block: 1px solid var(--color-border);
}

.section-title {
  margin: 0 0 48px;
  font-size: 24px;
  font-weight: 700;
  letter-spacing: 0.04em;
  position: relative;
  padding-left: 18px;
}

.section-title::before {
  content: "";
  position: absolute;
  left: 0;
  top: 50%;
  width: 6px;
  height: 22px;
  background: var(--color-accent);
  border-radius: 2px;
  transform: translateY(-50%);
}

.section-lead {
  margin: 0 0 32px;
  color: var(--color-fg-muted);
}

/* About info list */
.info {
  margin: 0;
  border-top: 1px solid var(--color-border);
}

.info-row {
  display: grid;
  grid-template-columns: 160px 1fr;
  gap: 24px;
  padding: 18px 4px;
  border-bottom: 1px solid var(--color-border);
}

.info-row dt {
  font-weight: 600;
  font-size: 14px;
  letter-spacing: 0.04em;
  color: var(--color-fg-muted);
}

.info-row dd {
  margin: 0;
  font-size: 15px;
}

.info-sub {
  display: block;
  margin-top: 4px;
  font-size: 13px;
  color: var(--color-fg-muted);
}

.info-note {
  margin: 24px 0 0;
  font-size: 13px;
  color: var(--color-fg-muted);
}

/* Cards */
.cards {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 24px;
}

.card {
  background: var(--color-bg);
  padding: 32px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
}

.card-title {
  margin: 0 0 12px;
  font-size: 17px;
  font-weight: 700;
}

.card-text {
  margin: 0;
  color: var(--color-fg-muted);
  font-size: 15px;
}

.card-index {
  margin: 0 0 12px;
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.2em;
  color: var(--color-fg-muted);
}

.card-list {
  margin: 20px 0 0;
  padding: 20px 0 0;
  list-style: none;
  border-top: 1px solid var(--color-border);
}

.card-list li {
  position: relative;
  padding-left: 18px;
  font-size: 14px;
  line-height: 1.9;
}

.card-list li::before {
  content: "";
  position: absolute;
  left: 0;
  top: 0.85em;
  width: 6px;
  height: 1px;
  background: var(--color-fg-muted);
}

/* Steps */
.steps {
  margin: 0;
  padding: 0;
  list-style: none;
  counter-reset: step;
  border-top: 1px solid var(--color-border);
}

.step {
  counter-increment: step;
  display: grid;
  grid-template-columns: 56px 1fr;
  gap: 24px;
  align-items: start;
  padding: 24px 4px;
  border-bottom: 1px solid var(--color-border);
}

.step::before {
  content: counter(step, decimal-leading-zero);
  grid-column: 1;
  grid-row: 1 / span 2;
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0.1em;
  color: var(--color-fg-muted);
  line-height: 1.9;
}

.step-title {
  grid-column: 2;
  margin: 0 0 4px;
  font-size: 16px;
  font-weight: 700;
}

.step-text {
  grid-column: 2;
  margin: 0;
  font-size: 14px;
  color: var(--color-fg-muted);
}

/* Lower page */
.page-head {
  padding: 72px 0 48px;
  border-bottom: 1px solid var(--color-border);
}

.page-title {
  margin: 0 0 16px;
  font-size: clamp(26px, 4vw, 34px);
  font-weight: 700;
  letter-spacing: 0.04em;
}

.page-lead {
  margin: 0;
  max-width: 640px;
  color: var(--color-fg-muted);
  font-size: 15px;
}

.prose h2 {
  margin: 48px 0 12px;
  font-size: 17px;
  font-weight: 700;
  letter-spacing: 0.02em;
}

.prose h2:first-child {
  margin-top: 0;
}

.prose p {
  margin: 0 0 12px;
  font-size: 15px;
  color: var(--color-fg-muted);
}

.prose ul {
  margin: 0 0 12px;
  padding-left: 20px;
  font-size: 15px;
  color: var(--color-fg-muted);
}

.prose .info {
  margin-top: 20px;
}

.revision {
  margin-top: 48px;
  padding-top: 20px;
  border-top: 1px solid var(--color-border);
  font-size: 13px;
}

/* Form */
.form {
  display: grid;
  gap: 20px;
  max-width: 560px;
}

.field {
  display: grid;
  gap: 6px;
}

.field label {
  font-size: 13px;
  font-weight: 600;
  letter-spacing: 0.04em;
  color: var(--color-fg-muted);
}

.req {
  display: inline-block;
  margin-left: 6px;
  padding: 1px 6px;
  font-size: 10px;
  font-weight: 700;
  color: #fff;
  background: var(--color-accent);
  border-radius: 3px;
  letter-spacing: 0.08em;
}

.field input,
.field textarea,
.field select {
  width: 100%;
  padding: 12px 14px;
  font: inherit;
  font-size: 15px;
  color: var(--color-fg);
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  outline: none;
  transition: border-color 0.15s ease;
}

.field input:focus,
.field textarea:focus,
.field select:focus {
  border-color: var(--color-accent);
}

.field select {
  appearance: none;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 12 8'%3E%3Cpath d='M1 1l5 5 5-5' fill='none' stroke='%235a5a5a' stroke-width='1.5'/%3E%3C/svg%3E");
  background-repeat: no-repeat;
  background-position: right 14px center;
  background-size: 12px;
  padding-right: 38px;
  cursor: pointer;
}

.form-note {
  margin: 0;
  font-size: 13px;
  color: var(--color-fg-muted);
}

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

.btn {
  justify-self: start;
  appearance: none;
  border: 0;
  padding: 14px 32px;
  font: inherit;
  font-size: 15px;
  font-weight: 600;
  letter-spacing: 0.06em;
  color: #fff;
  background: var(--color-accent);
  border-radius: var(--radius);
  cursor: pointer;
  transition: opacity 0.15s ease, transform 0.15s ease;
}

.btn:hover {
  opacity: 0.88;
}

.btn:active {
  transform: translateY(1px);
}

.btn:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

.form-status {
  margin: 0;
  min-height: 1.4em;
  font-size: 14px;
}

.form-status[data-state="error"] {
  color: var(--color-error);
}

.form-status[data-state="success"] {
  color: var(--color-success);
}

.hp {
  position: absolute;
  left: -9999px;
  opacity: 0;
}

/* Footer */
.site-footer {
  border-top: 1px solid var(--color-border);
  padding: 32px 0;
  background: var(--color-bg);
}

.footer-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.copy {
  margin: 0;
  font-size: 12px;
  color: var(--color-fg-muted);
  letter-spacing: 0.08em;
}

.footer-nav a {
  font-size: 12px;
  color: var(--color-fg-muted);
  text-decoration: none;
}

.footer-nav a:hover {
  color: var(--color-fg);
  text-decoration: underline;
}

/* Responsive */
@media (max-width: 640px) {
  .header-inner {
    height: 56px;
  }

  .site-nav {
    gap: 16px;
  }

  .site-nav a {
    font-size: 13px;
  }

  .hero {
    padding: 80px 0 64px;
  }

  .section {
    padding: 72px 0;
  }

  .section-title {
    margin-bottom: 32px;
  }

  .info-row {
    grid-template-columns: 1fr;
    gap: 4px;
    padding: 14px 4px;
  }

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

  .card {
    padding: 24px;
  }

  .step {
    grid-template-columns: 40px 1fr;
    gap: 16px;
    padding: 20px 4px;
  }

  .page-head {
    padding: 56px 0 40px;
  }

  .footer-inner {
    flex-direction: column;
    align-items: flex-start;
    gap: 10px;
  }
}

@media (max-width: 480px) {
  .brand-name {
    display: none;
  }

  .site-nav {
    gap: 14px;
  }

  .site-nav a {
    font-size: 12px;
  }
}