Forms 2.0 - Eliminate Gutter Width on 1 Field

I'm trying to eliminate the gutter width for one specific field on a Marketo 2.0 Form. I've tried the code below and haven't been able to get it to work, width is stuck at 10px. Can someone point me in the right direction?

.mktoGutter .mktohaswidth[for="C_Comments"] {

  width: 0px!important;

}