Hopefully ACF will consider adding this feature, but in the meantime this is what I’m using. Just include this CSS in your admin area and add the no-style
class to your Group field.
.acf-field-group.no-style {
padding: 0 !important;
}
.acf-field-group.no-style > .acf-label {
display: none !important; /* If you want the Group's label to show, remove this style */
}
.acf-field-group.no-style > .acf-input > .acf-fields.-border {
border: 0 !important;
}