0 Nov 27, 2014
Safari uses a strikethrough in showing invalid properties in style sheets. This is not documented, and there’s no tooltips to explain this multicolored line.
There are 2 known different strikethroughs, red and black.
Styles getting overridden by other styles are striked out in black:
But when it’s an invalid or supported property, or the value can’t be parsed, the strikethrough in the style sidebar is red: