Add CSS

[jungxjung]

Description of Pull Request

When I was deleting bootstraps, I accidentally deleted our main CSS , so our home page couldn't displayed properly.

Fixes #

Add CSS to our html

Please describe the pull request as one of the following:

• [x] Bug fix
• [ ] Breaking change
• [ ] New feature
• [ ] Documentation update
• [ ] Other

Tags

@Lancasterwu @ZachAndrews98 @Michionlion