Scroll to Top Plugin. Based on the idea of Jump To Top Plugin.
This plugin very lightweight and optimized to scroll to top of page.
If you're worried about load speed and optimization of your forum this plugin is for you.
And if you like it you'll find the way to thank me
You can see it in action here - https://www.planamigo.org
To modify block on scrolltop.css :
bottom:70px; - the displacement the button relative to the bottom of the page.
padding:25px 12px 5px; - with these values, you can adjust the size of the block.
(25px – top margin, 12px - left and right margins, 5px – bottom margin)
border-radius:7px; - rounding the edges of the block.
color:white; — color of label "top".
background:#808080; - color of the block.
You can translate "top" to your locale or even remove it.
Thats all, enjoy it.