theme: window close button touchup

- tone down the shading considerably to match the previous look

!453
4 jobs for !453 with wip/jimmac/closebutton-tweaks in 3 minutes and 58 seconds (queued for 2 seconds)
latest detached
Status Job ID Name Coverage
  Review
passed #243260
check_commit_log

00:01:42

 
  Build
passed #243261
build

00:01:31

 
  Test
passed #243262
test

00:00:43

passed #243263
test-pot

00:00:44