How the Heck? The Bootstrap 4 Beta thread

i can’t seem to get the ‘.d-none’ classes working in sage 8.5.3.

Preformatted textmessageOriginal: Invalid CSS after “…de text-hide();”: expected “}”, was “.d-none;

.featured-image-caption { 
    // display: none;
			// @include text-hide();
			.d-none;
    // 
    // .hidden-xs-up;
    // @include hidden-xl-down();
    // .d-none;
    // 
    // .hide;
}

Am i missing something obvious?