Improvements to and consistency in accessible hiding content. TODO: look into #3851 and create a mixin when using SASS.
Removed reference to old JS line number in popup CSS.
Only set font-size for mini style; margin, padding and icon position have em values.
Demos: Only need to set data-mini on the controlgroup, not on the buttons inside.
Select: Made sure we only move the native select from the screen in case of a custom select menu.
Controlgroup: Removed margin on controlgroup in bars. The bar already has padding.
Controlgroup: Same style for the controlgroup label (legend) as other labels.
Controlgroup: Removed font-size rules that breaks mini style.
Checkboxradio: Updated the CSS that hides the icon in horizontal controlgroups.
Checkboxradio: Accessibility. See also 3707c55.
Dialog: Switched to em values. Removed rule for content padding because it's already in core CSS.