import tinycss

def has_em_or_percent_font_size_definition(css):
    parser = tinycss.make_parser("page3")
    stylesheet = parser.parse_stylesheet(css)
    for rule in stylesheet.rules:
        for declaration in rule.declarations:
            if declaration.name == "font-size": #todo: try to detect font sizes defined under the `font` category name rather than font-size specifically
                token = declaration.value[0]    #todo: figure out what to do if there's more than one token. (can that ever even happen?)
                if token.unit in {"em", "%"}:
                    return True
    return False

test_cases = [
    ".foobar{font-size: 10em; background-color:blue} #bazqux{background-color:red}",
    "div{background-color: green}"
]

for idx, css in enumerate(test_cases):
    print("Test case #{}: {}".format(idx, css))
    if has_em_or_percent_font_size_definition(css):
        print("  Contains an em or % font-size definition")
    else:
        print("  Does not contain an em or % font-size definition")