prismjs.com has poor readability

That background image provides a very poor contrast.

![image](https://user-images.githubusercontent.com/73739153/140280350-1bb84880-e8c7-43a2-9416-b07fdfd29c43.png)


![image](https://user-images.githubusercontent.com/73739153/140280440-ecaab34b-beec-458c-b422-05b754a07e78.png)
