Underline styles were added.

[Ramin-Farhadi]

Description
Added two new underline classes for yellow backgrounds and white backgrounds.

Motivation and Context
Found out that this heavy-underline background is something that we are using regularly. I thought that's a good idea to have that as a class in order to prevent using custom style sheet every time.

How Has This Been Tested?
local

Types of changes

• 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:

• My code follows the code style of this project.
• My change requires an update to the documentation.
• I have updated the documentation accordingly.

[kimberspencer]

Please update classes to match what is in Athena, i.e. heavy-underline-secondary (https://ucf.github.io/Athena-Framework/utilities/colors/)