chromium/src/third_party/blink/web_tests/external/wpt/html/semantics/document-metadata/interactions-of-styling-and-scripting/stylesheet.py

from time import sleep
def main(request, response):
  if b"delay" in request.GET:
    delay = int(request.GET[b"delay"])
    sleep(delay)

  if b"stylesNotMatchingEnvironment" in request.GET:
    return u'h1 {color: brown;}'
  else:
    return u'h1 {color: purple;}'