Flexbox を使用して応答性の高い電卓のキーパッド レイアウトを設計するにはどうすればよいですか?

/* 1. Normalize styles */
* { box-sizing: border-box; }

/* 2. Flexbox container for the anomaly keys */
#anomaly-keys-wrapper {
  display: flex;
  width: 100%;
}

/* 3. First section of the anomaly keys (main keys) */
#anomaly-keys-wrapper > section:first-child {
  display: flex;
  flex-wrap: wrap;
  width: 75%;
}

/* 4. Individual keys within the main keys section */
#anomaly-keys-wrapper > section:first-child > div {
  flex: 1 0 33.33%;
}

/* 5. Double-width key within the main keys section */
#anomaly-keys-wrapper > section:first-child > div:nth-child(4) {
  flex-basis: 66.67%;
}

/* 6. Second section of the anomaly keys (special keys) */
#anomaly-keys-wrapper > section:last-child {
  width: 25%;
  display: flex;
  flex-direction: column;
}

/* 7. Double-height key within the special keys section */
#anomaly-keys-wrapper .tall {
  width: 100%;
  flex: 1;
}