If you're trying to preview a page and the preview window is very short like the screenshot above, you're likely running into a Chromium bug that results in iframes being rendered at 100px in height instead of 100%.
Workaround #1
Until this bug is resolved in a future release of Chrome / Edge, please try using another browser such as Firefox.
Workaround #2
If using a different browser is not an option or not preferred, you can also disable the enable-layout-ng flag in Chrome's settings:
- Open a new tab and visit the URL
chrome://flags - Search for
enable-layout-ng; this should return a single item named "Enable LayoutNG" as seen below:
- In the drop down menu to the right of that property, change the selection to Disabled.
- Re-launch Chrome (using the button that appears at the bottom right-hand corner of the page).