Critical css exclusion

Hi. Does the plugin have an option to add critical CSS that needs to be left alone? I have some SVG icons in my mobile menu that break the menu for a moment (is it FOUC) when “load CSS asynchronously” is enabled. Theme developer recommended adding critical CSS that needs to be left alone as below. Just not sure where I should insert it.

svg {
    height: 1em;
    width: 1em;
    top: .125em;
    position: relative;
    fill: currentColor;
}