Hi Kelly,
The only css I added was this: img{vertical-align:middle;margin: 5px}.esri-popup__content{margin:5px}.
I tested the css you suggested: .grid-container, .column-14, .column-12, .column-10, .column-18, .column-16, .column-6 {height:100%;width:100%;}. This made the desktop map disappear. The small device map was good:
With no css overrides the map on a small device only consumes 75% of the width as per this css setting:
The offending css (main.css) is this: .column-18 { width: 100%; max-width: 75vw;}. It is because the nearby side panel consumes the other 25% in desktop mode.
When I switch to responsive mode in Developer Tools (Chrome) get this:
[cid:image001.png@01D7F0E5.CCC4B720]
And the css (main.cs) now has two media queries.