Fix indicator alignment in MWCategoryItemWidget

We were setting the height to 2.25em which just happened
to be right, but it depended on the browser's default
line-height being a certain value. Now that that's changed
with unisolation, the alignment breaks.

Instead of using a magic value, use height: 100%; so it
takes the parent's height. We don't even have to make the
parent position: relative; because it already is.

Also change the width to 2em, which is a much more defensible
value than 2.25em. Previously 2.25em kind of made sense because
that was also the height (resulting in a square box), but
now we don't have that excuse any more.

Bug: 72962
Change-Id: Id617bfaafefd1fc1530fbee29be5d935ec486b92
Merge "Fix indicator alignment in MWCategoryItemWidget"