:root {
  --bg: #f6f7f9;
  --text: #1f2430;
  --accent: #2b6cb0;
  --card: #ffffff;
  --border: #dde1e8;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #161a22;
    --text: #e8eaf0;
    --accent: #6aa7e8;
    --card: #1f2430;
    --border: #333a49;
  }
}

* { box-sizing: border-box; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: "Hiragino Sans", "Yu Gothic", "Meiryo", sans-serif;
  line-height: 1.8;
}

main {
  max-width: 640px;
  margin: 0 auto;
  padding: 48px 20px;
}

h1 { font-size: 2rem; margin: 0 0 8px; }

section {
  margin-top: 32px;
  padding: 20px 24px;
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 10px;
}

h2 { font-size: 1.1rem; margin-top: 0; }

button {
  padding: 8px 18px;
  font-size: 1rem;
  color: #fff;
  background: var(--accent);
  border: none;
  border-radius: 6px;
  cursor: pointer;
}

button:hover { opacity: 0.85; }
button:focus-visible { outline: 3px solid var(--accent); outline-offset: 2px; }