css: change signup button background color

[akshayitzme]

change the bgcolor of the SignUp button thats defined in index.html

• change the bg color to match with the application theme
• theme colors are defined in css variables (--primary)
• ✨ Feel free to add your own changes !
• 💬 drop a comment if you like to take up this issue, so i can assign it to you.

[05Alston]

Can I work on this issue?

[SimonHoefling]

I would like to give it a try since I would like to Figur out how this works with issues on GitHub.

[akshayitzme]

I would like to give it a try since I would like to Figur out how this works with issues on GitHub.

@Simon-H01 go on :+1: