Why does assigning [dateClass] in mat-calendar have no effect?

I would like to add some custom stylings for certain days shown in the mat-calendar component from angular material. After a little bit of research I came across the dateClass property which seems to be suited for this task. Though no matter what I tried, the calendar always looks the same.

My current setup looks like following:

calendar.component.ts:

dateClass = (date: Date): MatCalendarCellCssClasses => { return 'my-date'; }

calendar.component.html:

<mat-calendar [dateClass]="dateClass"></mat-calendar>

calendar.component.css:

.my-date { background-color: red; }

Assigning [dateClass] seems to have no effect at all. I would expect all days to have a red background but the calendar always looks the same: Angular Material Calendar

Update:

OP pointed out encapsulation: ViewEncapsulation.None is also needed, as it was included in the stackblitz demo.

Original:

Your css is too broad, thus it's not getting applied to anything. To apply the css to date buttons, try this:

button.my-date {
  background: red;
}

Stackblizt demo

Result: