Reply To: How to change swatch display for size attribute

Try to add the following code snippet to the Custom CSS area in Theme Settings

.single-product-content .variations .swatches-select .text-only {
	border: 1px solid #090909;
}

.single-product-content .variations .swatches-select .active-swatch {
	background: #090909;
	color:white;
}