Ah I see the VM CSS is overwriting this. Just add an important declaration to the thirdparty.css file like follows:
@media screen and (max-width: 750px)
.width20, .width25, .width33, .width50, .width100, .vm-col-1, .vm-col-2, .vm-col-3, .vm-col-4, .vm-col-5 {
width: 98% !important;