I had this exact problem right now and after a little bit of looking I think I have a somewhat decent solution
You can target a mat-slider's thumb by using ::ng-deep so the code would would look like
::ng-deep .mat-slider-wrapper {
.mat-slider-thumb-container {
.mat-slider-thumb-label {
width: 50px;
height: 50px;
top: -62px;
right: -25px;
}
}
}
Where width and height can be changed to your desired values from their default of 28px
The top and right are a bit different, so the default right is -14px which is -(1/2) * width so you can use that to calculate your right. The top was a bit different. The default top is -40px so I just added -(height - defaultHeight) to it and got -62, however when testing this with a larger height value it didn't work as well as I expected so tinker with he top until you get the desired placement.