bug: doesn't parse `color: #67BA6A\9`

[wetneb]

Did you check existing issues?

• I have read all the tree-sitter docs if it relates to using the parser
• I have searched the existing issues of tree-sitter-css

Tree-Sitter CLI Version, if relevant (output of tree-sitter --version)

No response

Describe the bug

This is valid CSS:

.test { color: #67BA6A\9; }

Steps To Reproduce/Bad Parse Tree

Parse the above.

Expected Behavior/Parse Tree

Like without the escape sequence.

Repro

.foo {
  color: #67BA6A\9;
}

[wetneb]

This is a hack for IE, and I'm not sure exactly where those chars are allowed. This is reported as valid by the W3C validator:

.test {
  color: #fff\9;
  height: 500px\9;
  width:\9 !important;
}

[mohamedmansour]

this is definitely not needed, this was targeting IE9 for a CSS Hack, so should be treated as a ERROR. The \9 is a CSS escape sequence.

In this context, it’s not a valid part of a color value, but IE7 and IE8 would still parse and apply the rule. Modern browsers ignore it because #67BA6A\9 is not a valid color.