media query for mobile devices

Hi-

I am using the wedge theme and I have added the following (with no success) to the customizer to try and change the font color when the site is viewed from a phone:

/* Media Queries to adjust call to action text color with screen size */

@media
(max-device-width : 767px)
{ div.row call-to-action-wrapper.col-md-5.call-to-action.slogan.color
{ color:black!important }
}

I have white font selected in general, but I need black font on mobile devices as it switches to an opaque background.  Any suggestions?

Thanks!

-Thad