:root {
  --bg: #f9fafb;
  --card: #ffffff;
  --text: #1f2937;
  --heading: #111827;
  --muted: #6b7280;
  --border: #e5e7eb;
  --primary: #2563eb;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  padding: 0 16px 56px;
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
    "Hiragino Sans", "Noto Sans JP", "Helvetica Neue", sans-serif;
  font-size: 16px;
  line-height: 1.7;
  -webkit-text-size-adjust: 100%;
}

.wrap {
  max-width: 680px;
  margin: 0 auto;
}

header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  flex-wrap: wrap;
  padding: 20px 0 16px;
  border-bottom: 1px solid var(--border);
}

.brand {
  margin: 0;
  font-size: 15px;
  font-weight: 700;
  color: var(--primary);
  letter-spacing: 0.02em;
}

.lang {
  display: flex;
  gap: 6px;
}

.lang button {
  appearance: none;
  border: 1px solid var(--border);
  background: var(--card);
  color: var(--muted);
  border-radius: 999px;
  padding: 5px 12px;
  font: inherit;
  font-size: 13px;
  cursor: pointer;
}

.lang button[aria-pressed="true"] {
  border-color: var(--primary);
  color: var(--primary);
  font-weight: 700;
}

h1 {
  font-size: 24px;
  line-height: 1.35;
  color: var(--heading);
  margin: 28px 0 4px;
}

h2 {
  font-size: 17px;
  color: var(--heading);
  margin: 28px 0 8px;
}

h3 {
  font-size: 15px;
  color: var(--heading);
  margin: 20px 0 4px;
}

p,
li {
  margin: 8px 0;
}

ul {
  padding-left: 22px;
}

a {
  color: var(--primary);
}

.updated {
  margin: 0 0 8px;
  color: var(--muted);
  font-size: 14px;
}

.note {
  background: var(--card);
  border: 1px solid var(--border);
  border-left: 3px solid var(--primary);
  border-radius: 10px;
  padding: 12px 16px;
  margin: 20px 0;
}

.note p {
  margin: 4px 0;
}

.contact {
  display: inline-block;
  font-size: 18px;
  font-weight: 700;
  margin: 4px 0 8px;
}

footer {
  margin-top: 40px;
  padding-top: 16px;
  border-top: 1px solid var(--border);
  color: var(--muted);
  font-size: 14px;
}

footer a {
  margin-right: 14px;
}

body[data-lang="vi"] [lang="ja"],
body[data-lang="ja"] [lang="vi"] {
  display: none;
}