Markdown Preview Code Block's Text with Bad Contrast

[huacat1017]

Type: Bug
Does this issue occur when all extensions are disabled?: Yes (without Shiki)

The gray text in the picture above has a low contrast with light themes. The element might be .hljs-subst in highlight.css

The problem is worse in my theme because code blocks are also gray.

Steps to Reproduce:

1. Create a new Markdown file, then copy these:
   (the code may be not legal, I just simplified it which is from my extension's issue to make it easier to read.)

```bash
echo "deb [arg=$(TabcoDe)]"
```

2. Open the Preview of the file
3. The text is hard to see

See the issue huacat1017/huacat.pink-theme#2

VS Code version: Code 1.74.3 (97dec17, 2023-01-09T16:59:02.252Z)
OS version: Windows_NT x64 10.0.22621
Modes:
Sandboxed: No

System Info

Item	Value
CPUs	Intel(R) Core(TM) i5-8250U CPU @ 1.60GHz (8 x 1800)
GPU Status	2d_canvas: enabled canvas_oop_rasterization: disabled_off direct_rendering_display_compositor: disabled_off_ok gpu_compositing: enabled multiple_raster_threads: enabled_on opengl: enabled_on rasterization: enabled raw_draw: disabled_off_ok skia_renderer: enabled_on video_decode: enabled video_encode: enabled vulkan: disabled_off webgl: enabled webgl2: enabled webgpu: disabled_off
Load (avg)	undefined
Memory (System)	7.88GB (2.30GB free)
Process Argv	--crash-reporter-id 1984ce79-8f1f-47b0-88ab-e865d36f3187
Screen Reader	no
VM	0%

Extensions (43)

Extension	Author (truncated)	Version
language-x86-64-assembly	13x	3.0.0
easy-cpp-projects	ACh	2.0.0
fenix	ACh	1.1.5
project-manager	ale	12.7.0
doxdocgen	csc	1.4.0
jquerysnippets	don	0.0.1
vsc-material-theme	Equ	33.6.0
vsc-material-theme-icons	equ	2.5.0
better-cpp-syntax	jef	1.17.2
git-graph	mhu	1.30.0
vscode-language-pack-zh-hant	MS-	1.74.12140936
isort	ms-	2022.8.0
python	ms-	2022.20.2
vscode-pylance	ms-	2023.1.30
jupyter	ms-	2022.11.1003412109
jupyter-keymap	ms-	1.0.0
jupyter-renderers	ms-	1.0.14
vscode-jupyter-cell-tags	ms-	0.1.6
vscode-jupyter-slideshow	ms-	0.1.5
remote-ssh	ms-	0.94.0
remote-ssh-edit	ms-	0.84.0
remote-wsl	ms-	0.72.0
cmake-tools	ms-	1.13.40
cpptools	ms-	1.13.9
cpptools-extension-pack	ms-	1.3.0
remote-explorer	ms-	0.0.3
vetur	oct	0.36.1
material-icon-theme	PKi	4.23.1
java	red	1.14.0
swdc-vscode	sof	2.6.42
ayu	tea	1.0.5
open-in-browser	tec	2.0.0
pdf	tom	1.2.2
cmake	twx	0.0.17
windows-terminal	Tyr	0.7.0
intellicode-api-usage-examples	Vis	0.2.6
vscodeintellicode	Vis	1.2.30
vscode-java-debug	vsc	0.47.0
vscode-java-dependency	vsc	0.21.1
vscode-java-pack	vsc	0.25.7
vscode-java-test	vsc	0.37.1
vscode-maven	vsc	0.40.4
material-theme	zhu	3.15.6

(7 theme extensions excluded)

A/B Experiments

vsliv368:30146709
vsreu685:30147344
python383cf:30185419
vspor879:30202332
vspor708:30202333
vspor363:30204092
vswsl492cf:30256860
vslsvsres303:30308271
pythonvspyl392:30443607
vserr242cf:30382550
pythontb:30283811
vsjup518:30340749
pythonptprofiler:30281270
vshan820:30294714
vstes263cf:30335440
vscorecescf:30445987
pythondataviewer:30285071
vscod805:30301674
binariesv615:30325510
bridge0708:30335490
bridge0723:30353136
cmake_vspar411:30581797
vsaa593cf:30376535
pythonvs932:30410667
cppdebug:30492333
vsclangdf:30486550
c4g48928:30535728
dsvsc012cf:30540253
azure-dev_surveyonecf:30548226
vsccc:30610678
pyindex848cf:30577861
nodejswelcome1:30587005
2e4cg342:30602488
89544117:30613380
vscup:30628656

[mjbvz]

Closing this in favor of #91279, which I believe would fix this