The very basic version only allowing for one filter would be EasyEffects. If you want to use different filters for different programs you can install some LV2-plugins or bundles and then configure LV2-Plugins directly in pipewire (which is a bit of a pain) or use a GUI plugin-host like Calf and probably some patchbay (qpwgraph, patchmatrix, ...)
Or even better: try Carla, it may be a exactly what you want and can be remote controlled via MIDI or OSC
Well if you want modern CSS3-support or even JS you have to go for a browser. You could try NetSurf which is a very small & fast but only supports CSS2. Or Dillo, which is even smaller & faster (but also more limited in terms of CSS support)