(css) Escaped special character in selector class name breaks highlighting

**Describe the issue**

CSS class and ID selectors contain arbitrary strings (e.g. `.myclassname`), which can contain escaped special characters (e.g. `.foo\:myclassname` to match `class="foo:myclassname"`). Currently, the backslash that escapes a special character is not recognised by highlight.js as a valid part of the class name or ID.

**Which language seems to have the issue?**

css

**Are you using `highlight` or `highlightAuto`?**

`highlight`

**Sample Code to Reproduce**

```css
.dark\:hover\:bg-sky-500:hover {
--tw-bg-opacity: 1;
background-color: rgb(14 165 233 / var(--tw-bg-opacity));
}
```

Current highlighting:


**Expected behavior**

The escaped special characters (`\:`) should not interfere with the highlighting of the class name, but actual pseudoclasses (`:hover`) should still be highlighted.

GitHub:


VS Code:


**Additional context**

TailwindCSS makes extensive use of escaped characters in CSS selectors for its [modifiers](https://tailwindcss.com/docs/hover-focus-and-other-states).

Other special characters are escaped for features like [color opacity](https://tailwindcss.com/docs/text-color#changing-the-opacity):

```css
.dark\:hover\:bg-sky-500\/25:hover {
background-color: rgb(14 165 233 / 0.25);
}
```

…and [arbitrary values](https://tailwindcss.com/docs/adding-custom-styles#using-arbitrary-values):

```css
.dark\:hover\:bg-\[\#ff0000\]\/25:hover {
background-color: rgb(255 0 0 / 0.25);
}
```