White Plus / Minus Icon are not white on dark background color
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**Describe the bug**

Some white Icons appeal differently on some font sizes on dark background colour. It looks more light blue or grey. 
I noticed it on the plus and minus icon.

**Steps to Reproduce**

Reproduction Link: https://stackblitz.com/edit/vitejs-vite-kvithz?file=src%2FApp.tsx,src%2FApp.css,src%2Findex.css&terminal=dev
Zoom in and out and have a look at the plus and minus. 


**Expected behaviour**

Plus and Minus icon should be white no matter which zoom / dpi / size level. 

**Screenshots**

![image](https://github.com/phosphor-icons/homepage/assets/7667003/b2f75462-9b5b-482d-b3c3-be59e1b38db0)

**Context**

- OS: Windows 10
- Browser/Environment [Chrome, safari, node]
- Library  @phosphor-icons/react (I also had the issue with Angular)
- Version 2.1.4


**Additional notes**
This might also affect other icons. 

