The only CSS problem that I was able to see is that the navbar logo is extremely large.
From experimenting with npm run org, I see that the problem is no longer seen with:
--- a/sites/org/src/css/custom.css
+++ b/sites/org/src/css/custom.css
+.navbar__logo img {
+ height: 100%;
+}
+
I don’t understand how the CSS infrastructure of FreeSewing, Tailwind, React, and Docusaurus are set up or how they are supposed to interact, but the problem seems to be that, with CSS Cascade Layers enabled, the @layer docusaurus.infima {height: 100%;} gets superseded by @layer base {height: auto;}.
I filed PR #435 with the above code change, in case it is an appropriate fix.