Resizing images in ArcGIS Map Viewer pop-ups

[DavidMc_Laughlin]

Hi, I'm looking to re-size images that are being consumed in a pop-up in the AGOL Map Viewer. They're being added via an attribute URL and are too large for applications like the Zone Look-up.

I particularly like the customisation in the text content and was wondering is there a way to display and re-size through this?

Thanks.