Dashboard: remove not clickable spaces between icons and links in the "At a...

Dashboard: remove not clickable spaces between icons and links in the "At a Glance" panel. Also, some CSS cleanup.

Props 5um17 for the initial patch.
Fixes #27813.
Built from https://develop.svn.wordpress.org/trunk@35894


git-svn-id: https://core.svn.wordpress.org/trunk@35858 1a063a9b-81f0-0310-95a4-ce76da25c4cd