index.css

body{
  /* https://www.colordic.org/colorsample/2324 */
  background-color: rgb(234, 244, 252);
  /* https://googlefonts.github.io/japanese/#mplus1p */
  font-family: "M PLUS 1p";
}

h2, h3{
  /* https://www.colordic.org/colorsample/2072 */
  color: rgb(32, 55, 68);
  margin-bottom: 8px;
}

#box {
  text-align: start;
  margin: 16px;
}

#field table {
  border-collapse: collapse;
  font-size: 120%;
  font-weight: bold;
  display: inline-block;
}

#field table td {
  /* https://www.colordic.org/colorsample/2340 */
  background-color: rgb(233, 223, 229);
  /* https://www.colordic.org/colorsample/2072 */
  border: 1px solid rgb(32, 55, 68);
  width: 48px;
  min-width: 48px;
  height: 48px;
  min-height: 48px;
  display: table-cell;
  text-align: center;
  vertical-align: middle;
}

button {
  width: 200px;
  height: 48px;
  /* https://www.colordic.org/colorsample/2363 */
  background-color:rgb(192, 198, 201);
  font-weight: bold;
  text-align: center;
  border-radius: 8px;
}