LabelElement: Kill inline styles

We already toggle the .oo-ui-labelElement class on the parent element,
which makes it possible to apply different styles if the label is
visible or hidden.

Replicated the effect with CSS for code that depended on it.

Bug: 73156
Bug: 73677
Change-Id: I3a8fed4ebe4c0d56cb4cda25d42e30777ac035b7
Merge "LabelElement: Kill inline styles"