Fix persistent theme card hover state in IE11
Fix persistent theme card hover state in IE11

Fixes: CNVS-30103

Test plan:
- New UI only

- Open the main theme collection page in any
  version of IE11

- None of the theme cards should display the
  Open in Theme Editor button until the card
  thumbnail area is hovered over

- A11y note: screenreaders will ignore the
  whole thumbnail section of the theme card
  and use the theme name link below to get
  to the theme in Theme Editor

Change-Id: If8dfa47dcec07d8d60c3fc881274ef0316395ae4
Reviewed-on: https://gerrit.instructure.com/83480
Reviewed-by: Ryan Shaw <ea3cd978650417470535f3a4725b6b5042a6ab59@instructure.com>
Tested-by: Jenkins
QA-Review: Benjamin Christian Nelson <4a283f6b032925e40a485c88ede5597d7d65a090@instructure.com>
Product-Review: Chris Hart <b82b40b84a2f06957ec9caf1768340bd6b929cc4@instructure.com>

HotChalk/canvas-lms,matematikk-mooc/canvas-lms,sfu/canvas-lms,matematikk-mooc/canvas-lms,SwinburneOnline/canvas-lms,venturehive/canvas-lms,grahamb/canvas-lms,instructure/canvas-lms,grahamb/canvas-lms,venturehive/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,HotChalk/canvas-lms,SwinburneOnline/canvas-lms,instructure/canvas-lms,SwinburneOnline/canvas-lms,djbender/canvas-lms,fronteerio/canvas-lms,djbender/canvas-lms,dgynn/canvas-lms,SwinburneOnline/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,dgynn/canvas-lms,venturehive/canvas-lms,sfu/canvas-lms,grahamb/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,grahamb/canvas-lms,sfu/canvas-lms,fronteerio/canvas-lms,HotChalk/canvas-lms,dgynn/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,dgynn/canvas-lms,venturehive/canvas-lms,matematikk-mooc/canvas-lms,matematikk-mooc/canvas-lms,fronteerio/canvas-lms,sfu/canvas-lms,HotChalk/canvas-lms,fronteerio/canvas-lms,sfu/canvas-lms,grahamb/canvas-lms