CSS – woocommerce: variation price font size

plugin: woocommerce-product-addon
theme: Shop Isle Theme

Issue. Using woocommerce-product-addon with shopisle theme, the ‘add-on price’ FONT SIZE is the same as the same as the ‘product price’ FONT SIZE.

website
I need these 2 font sizes to be different. Product price 32px (standard for theme) is good, but I’d like 12px for the add-on price (far too big at 32px and looks odd).

I can change font size using custom css:

.single-product .amount {
	font-size: 12px;
	font-family: "Roboto Condensed", sans-serif;
	text-transform: uppercase;
	letter-spacing: 2px;
}

But this changes both prices. My coding knowledge is poor, but it seems both prices have the same class.

Is there a way I change font sizes independently; ideally through custom css? Thanks in advance.