The background of the <li> should be undefined, it shows green instead. This bug appeared on the last stable android webview and last stable desktop version of webkit and didn't exist before. https://jsfiddle.net/f557bLq4/1/
The CSS object model specification says "Mutating the declarations must set the style content attribute on the context object to the serialization of the declarations." https://drafts.csswg.org/cssom/#elementcssinlinestyle So it confirms this behavior is not wanted. A hotfix for webdevelopers is to mute the wanted property namely, element.style.backgroundColor = ''.
Aswell the ElementCSSInlineStyle forwards to cssText https://drafts.csswg.org/cssom/#cssstyledeclaration which says "2. Empty the declarations".
Added a more obvious test case to show the problem https://jsfiddle.net/f557bLq4/6/
Inline styles is now a thing because, and I see people get stumbled upon this issue in Safari more and more often (I counted 5 complaints this year alone in our 2200 members chat room). Setter polyfill, `setAttribute`, or `.style.cssText =` may be used instead, but I think this should be fixed to improve developer experience & spec compliance.
As of build 246014, `.style =` setter works as expected.
This issue was caused by spec-imperfect implementation of [PutForwards] extended attribute and was fixed in https://bugs.webkit.org/show_bug.cgi?id=172956. Test: web-platform-tests/WebIDL/ecmascript-binding/put-forwards.html