Added necessary sphinx theme.

4 jobs for docs in 7 minutes and 20 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #644305
build

00:03:19

passed #644306
buildgui

00:00:49

 
  Test
passed #644307
linting

00:00:46

passed #644308
tests

00:02:24

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