WordPress/wp-includes/blocks/calendar/style.css

.wp-block-calendar{
  text-align:center;
}
.wp-block-calendar tbody td,.wp-block-calendar th{
  border:1px solid #ddd;
  padding:.25em;
}
.wp-block-calendar tfoot td{
  border:none;
}
.wp-block-calendar table{
  border-collapse:collapse;
  width:100%;
}
.wp-block-calendar table th{
  background:#ddd;
  font-weight:400;
}
.wp-block-calendar a{
  text-decoration:underline;
}
.wp-block-calendar table caption,.wp-block-calendar table tbody{
  color:#40464d;
}