Resizing social icons

I cannot seem to find where I can change the size of the social icons? I am using the LSI in the header widget and I have used the inspector and have found the class it seems to be located in:

.icon-set-lsi_widget-3 a, .icon-set-lsi_widget-3 a:visited, .icon-set-lsi_widget-3 a:focus {
    border-radius: 5px;
    background: #ffffff !important;
    color: #0a0a0a !important;
    font-size: 20px !important;
}

If I change the font-size value in the inspector, the icons do resize, but when I try to override that CSS in the Customizer > Additional CSS it doesn't take effect.

I'm stumped?