Any question answered...

.qodef-media video {
	width: 100%;
	margin-top: 8px;
}
@media all and (max-width:1024px) {
	.qodef-portfolio-single-item.qodef-e.post-1887.portfolio.type-portfolio.status-publish.has-post-thumbnail.hentry.portfolio-category-exhibitions .qodef-col--4 {
	width: 100%;
}
	.single-portfolio .qodef-grid.qodef-layout--template > .qodef-grid-inner > .qodef-grid-item.qodef-col--8 {
		left: 0 !important;
		width: 100% !important;
	}
	.single-portfolio .qodef-grid.qodef-layout--template > .qodef-grid-inner > .qodef-grid-item.qodef-col-pull--8 {
		width: 100% !important;
		right: 0;
	}
	main.qodef-grid .qodef-grid-inner.clear {
	display: flex;
	column-count: 1;
	flex-direction: column-reverse;
}
}

Any indication based on the above how I could add borders only below a media item.

A dev I paid added the above to the CSS on my site so that media (images and video) had borders around it rather than just stacked immediately next to each other. Only now there's a border on the video, top and bottom, but not on the still images. I'm also concerned that adding a border on the top and bottom would lead to a kind of 'doubling up' of the border height. So presuming that border on the bottom edge of all media would be best. Is there somewhere I can test our alternative code without buggering up a live site?