Add .light class support to override custom properties

[garand]

I may explore making a PR for this, but it would be very useful I think to generate a .light class that can be used to set all of the properties to light mode again, in the same way that the .dark class works.

My use case is in dark mode, there are certain sections that I want to still force to be light mode. I can do the reverse of what I want by setting class="dark" on the parent of the section if the page is in light mode, but I can't do class="light" if the page is in dark mode.