[Feature Request] Changing Text Colour
## Background
In dark mode the text on that image is not clearly visible
https://www.eggjs.org/intro/egg-and-koa
[Image](https://camo.githubusercontent.com/d80cf3b511ef4898bcde9a464de491fa15a50d06/68747470733a2f2f7261772e6769746875622e636f6d2f66656e676d6b322f6b6f612d67756964652f6d61737465722f6f6e696f6e2e706e67)

## Proposal
Changing some color on their make user more clearly readable