The Viewport is the current visible area from the site, depending on your browser window size.
While most of your page layout will be relative to the page (the top left of the current page or breakpoint), sometimes you want it to be relative to the viewport.
This can be for example a top menu bar you want to stay in place:
Or an Intercom style bubble in the right hand corner:
⚠️ Fixed layout only works for elements that are not in a Stack or Grid
To enable viewport layout select any element and select layout: fixed in the properties panel:
You will see Viewport line appear and the bottom of your screen will be blued out. This line represents the bottom of what's visible within the viewport when the page is looked at. You can adjust it yourself for previewing (other fixed elements will respond to it). Once enabled, you can use standard pinning to adjust your layout, but now responsive to the viewport.