body {
  margin: 0;
  padding: 0;
  background: #000;
  min-height: 100vh;
  font-family: 'Noto Sans', 'Yu Gothic', 'Meiryo', sans-serif;
  display: flex;
  justify-content: center;
}

.container {
  background: #fff;
  width: 100vw;
  max-width: 400px;
  min-width: 0;
  padding: 24px 16px 32px 16px;
  box-sizing: border-box;
  display: flex;
  flex-direction: column;
  align-items: center;
}

.quiz-img {
  width: 100%;
  max-width: 320px;
  height: auto;
  margin-bottom: 24px;
  box-shadow: 0 1px 8px rgba(0,0,0,0.10);
}

input[type="text"] {
  width: 100%;
  max-width: 260px;
  padding: 10px 12px;
  font-size: 1.1rem;
  border: 1px solid #bbb;
  border-radius: 6px;
  margin-bottom: 18px;
  outline: none;
  box-sizing: border-box;
  text-align: center;
}

button#submit {
  width: 100%;
  max-width: 260px;
  padding: 12px 0;
  font-size: 1.1rem;
  background: #222;
  color: #fff;
  border: none;
  border-radius: 6px;
  cursor: pointer;
  transition: background 0.2s;
}

button#submit:hover {
  background: #444;
}

@media (min-width: 600px) {
  body {
    /* PC時は中央寄せ、左右黒額縁 */
    justify-content: center;
    align-items: center;
  }
  .container {
    margin: 40px 0;
  }
}