This reverts commit b7e0d9b1.

Found that by running css-lint on the code

Defines the highlight colour when selecting slide content using Mozilla
Firefox to match other browsers, instead of being the default colour.

This is similar to what is done in the "white" theme.

fix(PDF Export): Mark as important `width`, `height` and add `zoom` properties to fix CSS rules which were overrided by inline styles

I don't know if this is supposed to be this way ?

The `grunt css-themes` command now loops through all Sass files. There is no need to add the newly created file to the task list.