Thank you for advising us all.

There are a few additional points that are useful.
If you deconstruct the Candy Floss template and unlock the Pasteboard you will find the rectangle are centrally placed and have a very large negative x co-ordinate.

If you drop a colour onto the Pasteboard and then apply a linear Fill aligned vertically, you can double-click along the line and add any number of control points, each can have a colour applied.

The presentation is different but the final file size is much smaller.

The final technique is a reverse of the above in that you create a long thin pixel-exact image and drop that onto the unlocked Pasteboard and then right-click and set it as the Pasteboard background.

for all these approaches you can then select the background to be fixed, instead of scrolling.

Acorn