In 2188364-t the user reported that in the following CSS, the "fill" property gets stripped:

header.mobile-menu .mobile-logo .mobile-toggles .toggle-menu svg {
fill: #fff !Important;
}

I think that "fill" is not a valid property that can be used like this, but I'm not entirely certain. The property and the use of CSS for styling SVG elements is something that does indeed exist, but I think it can't be used in a stylesheet used for a website? http://tutorials.jenkov.com/svg/svg-and-css.html

Marking this as a bug for now until someone else can determine whether or not we should be stripping this value (because the value is not meant to be used in this way) or not.