The complete guide to Fluid UI

Increasing the page width or height in the page menu will automatically cause any pages to scroll (horizontally, vertically or both) when you preview.

Page settings menu

The dashed blue and white screen boundary marker will indicate where the page will start scrolling.

Screen boundary markers

Pinned widgets are frequently used with scrolling pages to make some content static while other content scrolls.

You may also want to know more about changing your resolution/device type or the difference between the screen size and page sizes to set your project up to your liking.