Multi-line string literals break CSS syntax highlighting

[Alex Ross]

Prerequisites

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Description

Multi-line string literals break CSS syntax highlighting.

Steps to Reproduce

1. Create a CSS file with this content

a::after {
	content: "long\
		value";
}

Expected behavior:

A multi-line string literal does not affect other rules.

Actual behavior:

There is no syntax highlighting after the backslash (any subsequent CSS is the same colour as the backslash itself).

Reproduces how often:

100%

Versions

From commit 339e960

Additional Information

Originally from @dansebcar in microsoft/vscode#125739