[Design] Change the style and align the back to top button properly!

[Manish-Kumarr]

Before:
The button is not aligned properly.

After:
Added background color and aligned properly

[Manish-Kumarr]

@mariobehling I want to work on it.

[abishekvashok]

Hey this requires changing a lot of other sites where this header is reused. I appreciate the amount of work you put in this issue, can you please take a look at open event. I am curious to see what you cna come up with there :)

[Manish-Kumarr]

@abishekvashok okay if you mention the websites then it will be easy for me.

[Manish-Kumarr]

So, There was no back-to-top button, that is what I added here and we can reuse this same code in all the subdomains.
Here is the demo hope you like this @abishekvashok @mariobehling
https://manish-kumarr.github.io/fossasia-demo/

I want to work on all the subdomains.

After

Before

[Manish-Kumarr]

@abishekvashok please have a look.