These rely on the default Szurubooru theme to be used. You can use these with any userstyle browser extension, or integrate them into your szurubooru builds.
I recommend the Stylus extension. Firefox | Chromium Browsers | Git Repo
FOR USERSTYLES: Remember to edit the first line with your booru's IP address or domain.
@-moz-document domain("szuru.example.com") {
...
}
I provide two variants, Vanilla & Mosaic. Vanilla keeps to the default grid, and Mosaic allows variable width.