So this default stuff is located in ox-html.el I'm guessing. If I wanted to override the default behavior of putting a border and a gray bar around a source code block, there really isn't a specific Org Export HTML customization entry for that. I'd just have to figure out how to override the specific css in the generated default css at the top of my exported HTML, correct? I'm not sure which thing I'm supposed to tweak per this but it must be one of them. In the meantime, I stuck this into my stylesheet.css and it seemed to work. Is the usual thing to simply turn off ox-html and roll your own?