Added loading GIF to the GET CSS button

[theshubhagrwl]

Description

This a small and essential change that I have made.

Motivation and Context

After clicking the Get CSS button, the user does not get any feedback, so adding a loading button satisfies the user that the app is working properly.

How Has This Been Tested?

I have tried it by clicking the button a couple of time.

Screenshots (if appropriate):

This is how the button looks in the loading stage.

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have added tests to cover my changes.
• [x] All new and existing tests passed.

[sansyrox]

Looks good! I am marking it as intermediate!