Icons preloading introduced in 247755c5 overrides entire background
property, not just background-image. On 2x screens (and anywhere else
where svg icons need to be scaled) icons need property `background-size:
contain` to be displayed correctly. This previously came from
`.icon-css` class but have been overriden by code generated in
`svgicon`, so to fix this, these properties need to be added to the
`svgicon`.
