Editing Template:Multiple image/styles.css

/* {{pp-template}} */
/* this is a block */
.multiimageinner {
	display: flex;
	flex-direction: column;
}

.trow {
	display: flex;
	flex-direction: row;
	clear: left;
	flex-wrap: wrap;
	width: 100%;
	box-sizing: border-box;
}

/* this is a cell */
.tsingle {
	margin: 1px;
	float: left;
}

.theader {
	clear: both;
	font-weight: bold;
	text-align: center;
	align-self: center;
	background-color: transparent;
	width: 100%;
}

.thumbcaption {
	background-color: transparent;
}

.text-align-left {
	text-align: left;
}

.text-align-right {
	text-align: right;
}

.text-align-center {
	text-align: center;
}

@media all and ( max-width: 720px ) {
	.thumbinner {
		/* not !important usage can be removed when these are no longer inline styles
		inside Template:Multiple image and media query using min-width is introduced */
		width: 100% !important;
		box-sizing: border-box;
		max-width: none !important;
		align-items: center;
	}
	.trow {
		justify-content: center;
	}
	.tsingle {
		/* not !important usage can be removed when these are no longer inline styles
		inside Template:Multiple image and media query using min-width is introduced */
	    float: none !important;
	    max-width: 100% !important;
	    box-sizing: border-box;
	    text-align: center;
	}
	.tsingle .thumbcaption {
		text-align: left;
	}
	.trow > .thumbcaption {
		text-align: center;
	}
}