Hmm. It looks like this:
And this is the result:
(Get the Elements display by right-clicking the red Taken By and select Inspect. Then click on the line above where the nx-basicfieldeditor-item-label element appears. The Styles panel on the right may show something being overridden.)
(I did notice I was testing with a reference field, so I verified that the same method is working with String and Template fields.)
Other than the css being overridden by something else, the one thought that does come to mind is that the CSS Class entered in the field editor property should be spouseInfo and not .spouseInfo, and is presumably case-sensitive. The name of the CSS Inline resource does not actually have to match anything. You can even put multiple classes into a single resource.
