Theme thumbnails flicker on hover

[Clorith]

When hovering over the thumbnails in the 1st or 2nd column in the new theme directory they seem to resize horizontally within their container by a few pixels then shrink back to the original size.

This doesn't happen on the 3rd column.

Only seems to occur in Chrome 40 (also tested in FF 36 and IE11 where the stutted doesn't happen) on Windows.

It seems to be caused by the transition rule on .theme-browser .theme .theme-screenshot img (themes.css line 150), that gets re-triggered when we apply the overlay to the thumbnail.

[Clorith]

After ab it of testing, I'm not seeing any effect of having the transition rule on this particular selector (perhaps I'm missing something?), so removing it shouldn't be a problem and would solve this, but someone who knows the purpose of the rule might want to chime in.

[obenland]

In 1413:

WP.org Themes: Prevent thumbnail flicker in Chrome.

This was removed from the wp-admin theme-install screen in ​[core31316].

Fixes #917.