Create global color styling and apply to buttons

[krsnamara]

Summary

Create CSS variables in the index.css file to be accessed through out the app. Also currently there are no global set styles for buttons. In this issue you will create a basic standard styling to be applied across the app. Once the styles have been defined in index.css, they can be applied in the app and adjusted to fit individual use cases.

Acceptance criteria

• Create CSS variables with brand colors including hovers
• Define at the index level how button inheritance style will look
• Confirm that the styles are applied in the app correctly

Notes

Sub-issue of #14