Fix anchor tags scrolling to the wrong place when fixed navbar is enabled

[ButteredCats]

Fixes #79

The site didn't account for the navbar being there when it jumps somewhere. Adding the scroll-padding-top attribute fixes this by telling the browser to scroll further.

I had to add the fixed_navbar class to html as otherwise you'd have to add it to each element you're jumping too, which would be far more complicated and would require actual code.
Every other reference to the fixed_navbar class in style.css is targeting the class for a specific type of element, so it doesn't have any extra effects but might be something to keep in mind if any more work is done with the class.

[sigaloid]

Thanks! 😄