Seeing as this is still relatively recent in terms of interest, I thought Id share my experience of this.

I tried the above methods and ended up implementing something that offers the best of both worlds.

The first method (individual custom field application) works great. but I had concerns around the required extra vigilance in administration and tracking of which fields have this applied (already several hundred fields in operation).

Also required an update in behaviour that ensured more vigilant confirmation testing of every field's presentation moving forward.

The second method (global application) by Terry works great for all fields by targeting the <p> elements, but my experience was that text would spill outside of the request form div container. Unless I added manual line breaks to handle the word wrap.
This quickly made my older fields look chaotic and messy.

So if anyone wants to mix these two great ideas, the following is something I have applied at a global level in the style.css:

/***** Global Request Form Customization *****/
.request-form p,
.request-form .hint {
white-space: pre-wrap !important;
word-wrap: break-word !important;
}

I placed the code in the same region as all of the "My Activities and New Request"" style handlers.
(greyed code for orientation purposes only)

Example is in a query initiated workflow I am implementing for our HR department as they transition from shared mailbox task culture to Zendesk.
As you can see, this means I can add no-code line breaks in field descriptions whilst conveniently handling any text wrap spill.
Ill provide further feedback if this bites me, but “so-far so-good”.

The field set-up:

The finished product:

Hope this helps someone some day.