Fields Selection Screen Size

Hello, Jason!
 
Thank you for reaching out to us.
 
Kindly note that it is possible to resize the FieldList pop-up by overriding some CSS styles, for example:

#fm-pivot-view .fm-fields-view{
    width: 100%!important;
}

 
You can also use CSS @media queries to adjust the necessary width to different screen sizes:

@media (max-width: 760px) {
  #fm-pivot-view .fm-fields-view {
    width: 100% !important;
  }
}

We have prepared a JSFidlle example for illustration: https://jsfiddle.net/flexmonster/zgsj92Lt/.
Please, press the Fullscreen button on the Toolbar to see the FIeldList on the maximum screen width.
 
Hope you will find our answer helpful.
 
Regards,
Solomiia

Hello, Jason!

Thank you for your swift feedback.

We are glad to hear that the suggested approach works for your case.

Feel free to contact us if any other questions arise.

Regards,
Solomiia