Sorry, but that is not brutalism. That is just a badly designed page. Small grey font is pretty much the opposite of brutalism. So are small pastel colored buttons with rounded corners.
It looks like a bootstrap theme but with all spacings done wrong.
Brutalism is in the eye of the beholder, of course, and any talk of Brutalism on the web is an exercise in analogy given that the core mantra of architectural Brutalism was to stay "true to the materials" and for pixels it's hard to be "false" with them.
The variation of the theme that just uses HTML2/3-esque TABLEs and table borders is definitely more directly evocative of that spirit, stripping away CSS for just the brutal truth of classic HTML design. I tried to find a direct link to that version of Brutaldon's theme, but am not sure where to find one, and searching one's Mastodon feeds from weeks seems to be tougher than I expected.
It looks like a bootstrap theme but with all spacings done wrong.