navigation underline color

I've changed the color of the navigation font but I cannot find any code to change the underline color?
Here's the code I used to change font color:
.sp-megamenu-parent > li.active > a {color: #F98100;}
}

Can someone show the code for the underline? I'm using Folium Template.
Is it possible to make the underline thicker and/or longer?

Thanks