Default CSS

enable custom CSS if and only if page does not define any styles in <head>

Enable your custom CSS if and only if page does not define any styles in <head>.

This userscript refers to sp.css from https://github.com/susam/spcss/ project, but you can easily change the link to another style sheet.

Example page without any styles in <head>: https://www.gnu.org/software/termutils/. The script could also be useful for viewing offline documentation, e. g. /usr/share/doc/bash/bash.html

Screenshots show the same page "before" and "after"