I noticed two issues in Views UI CSS, in the views_ui module and Seven theme.
First, #edit-displays-preview-controls has been removed, way back in #1104204: Separate preview and main UI to prevent wide previews from destroying UI, but there are some CSS rules still referencing it. Trying to re-apply those rules by changing them to #views-ui-preview-form broke the Views UI preview form, so it's best to remove them.
Second, views-ui-rearrange-filter-form is no longer used as form id, but a class. So, some CSS styles no longer applied in the Filter Criteria Rearrange Form. I changed the rules into using the class, and added screenshots:
Before changing ids to class

After changing ids to class

Comments
Comment #1
herom commentedComment #2
BarisW commentedThanks, looks good. I can't see any visual differences. Patch looks good to go. +1
Comment #3
lewisnymanFrom a code point of view this looks good, it's been manually tested so RTBC
Comment #4
webchickSince this is changing CSS outside of Seven, can we get verification that this continues to look right in Stark/Bartik?
Comment #5
lewisnymanHere are some screenshots from Bartik and Stark:
Comment #6
webchickGreat, thanks!
Committed and pushed to 8.0.x.