Hi Ian,
In order for the button to remain visible at all times, it need fixed positioning.
Unfortunately, there’s no way to apply the fixed positioning to specific elements in the browser (sidebars etc..) – fixed positioning is always relative to the entire screen.
Of course, you can adjust the positioning, but remember how it will look on smaller screens/phones:
.generate-back-to-top {
bottom: 30px; /* 30px from the bottom of the screen */
right: 30px; /* 30px from the right of the screen */
}