🐛 Bug Report

Sometimes the color is missing when running yarn build

Have you read the Contributing Guidelines on issues?

YES

To Reproduce

If possible, use https://new.docusaurus.io to create a CodeSandbox reproducible demo of the bug.

(Write your steps here:)

1. Add below code in custom.css

.menu .menu__link.menu__link--active:not(.menu__link--sublist) {
  border: 1px solid rgba(167, 167, 167, 0.2);
}

1. yarn build
2. Search .menu .menu__link.menu__link--active:not(.menu__link--sublist) in build directory

Expected behavior

.menu .menu__link.menu__link--active:not(.menu__link--sublist) {
  border: 1px solid rgba(167, 167, 167, 0.2);
}

Actual Behavior

Your Environment

• Public source code:
• Public site url:
• Docusaurus version used: 2.0.0-alpha.70
• Environment name and version : node v14.15.5 (npm v6.14.11)
• Operating system and version (desktop or mobile): macOS big sur 11.1

Reproducible Demo

If possible, use https://new.docusaurus.io to create a CodeSandbox reproducible demo of the bug.

https://codesandbox.io/s/interesting-night-ze576?file=/src/css/custom.css