It would be great if the Theme Styles section had the option to arrange theme styles hierarchically, so that one theme style can inherit settings from a parent theme style as its default. Visually, it could look pretty much just like the Structure panel that allows you to arrange elements on the page.
For example, I might set a theme style with the condition sitewide as the root theme style, and underneath this (as a child theme style) I might add a theme style for blog posts. Within the root theme style I might set the font size of header elements, and the width of the page. Within the child theme style, I might only change the header font sizes. The root theme style would automatically be used as the default for the blog post theme style, unless I explicitly need to make a change to a setting in the child theme style. However, if I moved the blog post theme style out from under the sidewide theme style and made it a root theme style as well (not inheriting from anything), the default values would be the Bricks Builder defaults, instead of the sitewide theme style settings.
Hopefully that makes sense.