Change Checkbox Size in Angular Material Selection List

Yes, the checkmark is just a pseudo element within the checkbox. You can override it's styles the same way as with the box itself.

For your case with the 10px box size the following CSS would work (for other sizes the values need to be adjusted):

.mat-pseudo-checkbox-checked::after {
    top: 0px;
    left: -1px;
    width: 6px;
    height: 2px;

With Angular 7 I succeeded with:

mat-checkbox ::ng-deep .mat-checkbox-inner-container {width: 30px;height: 30px;}

I was facing the similar issue and tried the below CSS, which seems to work in Angular 8:

::ng-deep .mat-checkbox .mat-checkbox-inner-container {
    width: 30px;
    height: 30px;

I have added a sample width and height; please customize these to what you need.