[FEATURE] CSS variables in theme.css should be namespaced.

[parmvirthind]

This library defines a variety of CSS variables in theme.css.
A lot of these variables are common names that could collide with other libraries (ex. --background-color).
Since these variables are applied to the :root, they will apply to any project using this library. (See related issue here)

Describe the solution you'd like
We should update these to be name-spaced in some manner. Maybe a pre-fix of spk. (ex. --spk-background-color)