📄 style.css

/**
 * Colors
 */
.wp-block-calendar {
  text-align: center;
}
.wp-block-calendar th,
.wp-block-calendar td {
  padding: 0.25em;
  border: 1px solid;
}
.wp-block-calendar th {
  font-weight: 400;
}
.wp-block-calendar caption {
  background-color: inherit;
}
.wp-block-calendar table {
  width: 100%;
  border-collapse: collapse;
}
.wp-block-calendar table.has-background th {
  background-color: inherit;
}
.wp-block-calendar table.has-text-color th {
  color: inherit;
}
.wp-block-calendar :where(table:not(.has-text-color)) {
  color: #40464d;
}
.wp-block-calendar :where(table:not(.has-text-color)) th,
.wp-block-calendar :where(table:not(.has-text-color)) td {
  border-color: #ddd;
}

:where(.wp-block-calendar table:not(.has-background) th) {
  background: #ddd;
}