Html sanitize css property background-repeat

[lukapor]

Attached file sample htmlBackgroundNoRepeat.html has css property background-repeat. When I sanitize html, property is gone and sanitize html is broken (cleanHtmlBackgroundNoRepeat.html).
attachedFiles.zip

[mganss]

Here's the original HTML (please post such short snippets directly in the issue comments):

<div style="font-size: 12pt; font-family: 'Segoe UI';">
    <div fr-original-style="width: 400px; height: 400px; background-image: url('https://user-images.githubusercontent.com/42636057/96471112-437d9a80-122f-11eb-86c2-f30d9b0c8054.png'); background-repeat: no-repeat;"
        style="width: 400px; height: 400px; background-image: url('https://user-images.githubusercontent.com/42636057/96471112-437d9a80-122f-11eb-86c2-f30d9b0c8054.png'); background-repeat: no-repeat;">
        test</div>
</div>

This is a bug that occurs because the parser unravels shorthand CSS properties such as background-repeat to their longhand representations such as background-repeat-x and background-repeat-y. I'll add the missing longhand values to the default configuration. In the meantime, you can add the missing values yourself by doing

sanitizer.AllowedCssProperties.Add("background-repeat-x");
sanitizer.AllowedCssProperties.Add("background-repeat-y");

Do you mean this by broken or do you think there is an additional issue? It seems that in the attached output file the newlines are missing but I can't repro that.

[mganss]

While the above is true as a cause for the issue it seems there aren't officially CSS properties background-repeat-x and background-repeat-y. Investigating.

[mganss]

Chromium implements this partially (you can still see it in dev tools) and there were discussions to add it to the specification but it was decided against AFAICT: w3c/csswg-drafts#116
I'll add the longhands nonetheless to solve this issue.