Repository: vscode
Issue: [css] support nth-child-of
Labels: feature-request,css-less-scss

Type: <b>Bug</b>

1. Enter the following valid style definition in a CSS file. The CSS parsing validator will fail on the "of" keyword and show the file as containing errors.

```
tr:nth-child(3n+3 of :not(.hidden)) {
  background-color: lightgrey;
}
```

Editor appears like this:

![image](https://user-images.githubusercontent.com/812777/236285003-32877897-c1db-4989-b831-147b688ede62.png)

And the file tree appears like this:

![image](https://user-images.githubusercontent.com/812777/236286674-7b189c7b-5e6f-49ca-9b95-bd00b1a1d2b6.png)

However, when replacing the number with the "even" or "odd" keyword, parsing works correctly:

![image](https://user-images.githubusercontent.com/812777/236285972-ee4a1afe-b32a-42b4-be81-02291900c4de.png)

This is valid CSS according to this Chrome Developer article: https://developer.chrome.com/articles/css-nth-child-of-s/


VS Code version: Code 1.77.3 (704ed70d4fd1c6bd6342c436f1ede30d1cff4710, 2023-04-12T09:16:02.548Z)
OS version: Windows_NT x64 10.0.22621
Modes:
Sandboxed: No

<details>
<summary>System Info</summary>

|Item|Value|
|---|---|
|CPUs|Intel(R) Core(TM) i7-8850H CPU @ 2.60GHz (12 x 2592)|
|GPU Status|2d_canvas: enabled<br>canvas_oop_rasterization: disabled_off<br>direct_rendering_display_compositor: disabled_off_ok<br>gpu_compositing: enabled<br>multiple_raster_threads: enabled_on<br>opengl: enabled_on<br>rasterization: enabled<br>raw_draw: disabled_off_ok<br>skia_renderer: enabled_on<br>video_decode: enabled<br>video_encode: enabled<br>vulkan: disabled_off<br>webgl: enabled<br>webgl2: enabled<br>webgpu: disabled_off|
|Load (avg)|undefined|
|Memory (System)|31.79GB (4.95GB free)|
|Process Argv|--crash-reporter-id 1d9325a9-6575-4e45-8014-8aa12809d09c|
|Screen Reader|no|
|VM|0%|
</details><details><summary>Extensions (10)</summary>

Extension|Author (truncated)|Version
---|---|---
aws-toolkit-vscode|ama|1.71.0
gitlens|eam|13.5.0
copilot|Git|1.84.51
todo-tree|Gru|0.0.226
vscode-cfml|Kam|0.5.4
vscode-docker|ms-|1.25.0
remote-containers|ms-|0.288.1
vscode-yaml|red|1.12.2
markdown-preview-enhanced|shd|0.6.8
vscode-todo-highlight|way|1.0.5


</details><details>
<summary>A/B Experiments</summary>

```
vsliv368cf:30146710
vsreu685:30147344
python383:30185418
vspor879:30202332
vspor708:30202333
vspor363:30204092
vstes627:30244334
vslsvsres303:30308271
vserr242cf:30382550
pythontb:30283811
vsjup518:30340749
pythonptprofiler:30281270
vshan820:30294714
vstes263:30335439
pythondataviewer:30285071
vscod805cf:30301675
binariesv615:30325510
bridge0708:30335490
bridge0723:30353136
cmake_vspar411:30581797
vsaa593cf:30376535
pythonvs932:30410667
cppdebug:30492333
vsclangdc:30486549
c4g48928:30535728
dsvsc012cf:30540253
pynewext54:30695312
azure-dev_surveyone:30548225
nodejswelcome1cf:30587006
282f8724:30602487
pyind779:30671433
89544117:30613380
pythonsymbol12:30671437
2i9eh265:30646982
6233i204:30672705
vsccsb:30705552
azdwalk:30721579
pythonms35:30701012
pythonfmttext:30716742
pythonclientmvcf:30725893

```

</details>

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