WPML larger flag selector

Hello,

I need to increase the size of the flags in the header for the WPML language selector. Here is what I changed to enlarge the flags.
– I uploaded a US & Spanish flag as 36px x 24px (instead of the default 18×12)
– Added this CSS

.avia_wpml_language_switch li .language_flag img {
 		width: 36px;
		height: 24px;
}

The flags are now bigger but they are blurry. It appears that it’s using the CSS to increase the images from 18×12 instead of presenting the 36px x 24px image.

Thanks for your help!