Use explicit strip widths and button heights for the mixer
The goal is to preserve a consistent layout and sizing of the buttons.
Button height should not resize based on text, because font styles differ and this leads to inconsistent button heights
Button width should not be based on text or font size;  instead, font size just determines how many chars will be visible in the button
There are some elements of the editor page which _do_ scale based on the text width, and thats probably sensible because the text is predefined, and needs to fit