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## Summary of the Pull Request
As discussed in #6293 , this PR adds a fade animation to button background when pointer hover ends
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## References
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## PR Checklist
* [x] Closes#6293
* [x] CLA signed. If not, go over [here](https://cla.opensource.microsoft.com/microsoft/Terminal) and sign the CLA
* [ ] Tests added/passed
* [ ] Requires documentation to be updated
* [x] I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: #xxx
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## Detailed Description of the Pull Request / Additional comments
Added storyboarded coloranimations to the visualstategroup of captionbuttons
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## Validation Steps Performed
Tested manually
a34f1e2ad4