* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  font-family: sans-serif;
  background: #f5f7fa;
  color: #333;
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

/* ヘッダー */
header {
  background: linear-gradient(135deg, #4f46e5, #3b82f6);
  color: #fff;
  padding: 2rem;
  text-align: center;
}

/* メイン */
main {
  flex: 1;
  display: flex;
  justify-content: center;
  align-items: center;
}

/* カード */
.container {
  background: #fff;
  padding: 2rem;
  border-radius: 12px;
  box-shadow: 0 8px 16px rgba(0,0,0,0.05);
  text-align: center;
}

/* ボタン */
button {
  margin-top: 1rem;
  padding: 0.7rem 1.4rem;
  border: none;
  border-radius: 8px;
  background: #4f46e5;
  color: #fff;
  cursor: pointer;
  font-size: 1rem;
}

button:hover {
  background: #3730a3;
}