Why aren't my base styles updating in the preview?
If you're removing styling from a base style, those styles still apply until you have saved the base style.
When removing CSS properties from base styles the preview does not update to reflect your changes until you have saved the style. This is because you are styling a base element and the preview cannot display what a base style will appear like when properties have been removed, until they have been removed and the stylesheet generated.
This is different to Custom styles as these are classes. For these, the preview uses a preview class which does not rely on the actual class being generated.