[IMPROVE] Message Box icons have hover effect

[apurv-1]

• I have read the Contributing Guide.
• I have signed the CLA.
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works (if applicable)
• Any dependent changes have been merged and published in downstream modules
• I have added necessary documentation (if applicable)

Proposed changes (including videos or screenshots)

Added hover effect for changing the colour of the icon on MessageBox.

bandicam.2021-03-11.03-54-24-620.mp4

Issue(s)

fixes #21068

Steps to test or reproduce

Further comments

[apurv-1]

@Sing-Li @dougfabris Please have a look! Thanks.

[aditya-mitra]

@apurv-1 Can add a closes under the Issues of this pr?
Something like this : Closes #21068.

This would not only close the issue on this pull request being merged but also be helpful while seeing the issues page indicating that this issue already has a pull request.

If you want to know more about such keywords, please check it out here. 😃

[apurv-1]

Yeah, Sure! Thanks for the suggestion. 😃

[dougfabris]

@apurv-1 Recently we refactor our Message Composer and it already fixes it! #27566
Because of that, I'm closing this one, thank you so much for your help!