Examples: Improve GUI of pathtracer demo. (#24862)
Examples: Improve GUI of pathtracer demo. (#24862)

* Examples: Improve GUI of pathtracer demo.

* Update webgl_renderer_pathtracer.html

* Update webgl_renderer_pathtracer.html

Co-authored-by: mrdoob <59bd0a3ff43b32849b319e645d4798d8a5d1e889@mrdoob.com>
mrdoob/three.js,mrdoob/three.js