As a suggestion (not yet validated with WMF) the size of binary inputs (radio buttons, check boxes) should be relative (1:1) to the line-height applied to the accompanying label text. In order to achieve that with the least amount of code, we could use the css4 size unit 'lh' or 'rlh'.

This solution could also be applied to properly align icon buttons (which size, after all, also matches the 20px line-height applied to button labels).

Note: the 'lh' unit is experimental and, as such, not yet supported by any browser.