In `rasterizeAnnotationLayer` we load the source CSS files directly, so
these are not processed by Autoprefixer. Since the prefixed rules have
now been removed from the source CSS files, we must manually provide one
prefixed rule that Chrome needs in the overrides CSS file for checkbox
and radio button rendering to work in the reference tests.
reference tests
This patch allows us to use the common styles as used by the viewer as a
baseline for the annotation layer reference tests. They are extended
with a small set of overrides to ensure that all elements are visible
during the test.
The overrides file now only contains the absolutely necessary rules to
make all elements visible and is therefore no longer an almost verbatim
copy of the common styles.