ihk24/templates/source/sass/partials/vendor/_jquery-datepicker.scss

.ui-datepicker{
  .ui-datepicker-calendar{
    .ui-datepicker-current-day{
      background-color: $color-primary-light-03;
      background-color: var(--theme-color-primary-dimmed-02,  $color-primary-light-03);
    }
  }
}