I want you to act as a web developer and please write some code for me to create a “Go to top” button for the website.

I want you to act as a web developer and please write some code for me to create a “Go to top” button for the website.
Design Style: Features a circular floating button design with a background in the theme color (such as blue or the brand’s color) and a white arrow icon.
Position: Fixedly positioned in the lower-right corner of the viewport, 20px from the bottom and the right edge.
Shading: Features gentle shading, giving the impression that it is floating above the page.
Icons: Use SVG icons or font-based icons, with the arrow pointing upwards.