box-sizeing is lost when css is parsed

[jogibear9988]

Bug Report

Prerequisites

• [x] Can you reproduce the problem in a MWE?
• [x] Are you running the latest version of AngleSharp?
• [x] Did you check the FAQs to see if that helps you?
• [x] Are you reporting to the correct repository? (there are multiple AngleSharp libraries, e.g., AngleSharp.Css for CSS support)
• [x] Did you perform a search in the issues?

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Descriptionif you parse box-sizing it is completely removed from the css:

Steps to Reproduce

Try this snippet:

        var source = "* { box-sizing: border-box; }";
        var css = ParseStyleSheet(source);
        var text = css.Rules[0].CssText;

Expected behavior:

the text to be as nearly the same as the input one

Actual behavior:

i got:

   * { }