Underlined Active Linked Pages in Navigation

I'm trying to figure out how to make the linked page that I click on in my navigation bar underlined while it's active. Currently, it's only the Homepage that remains underlined when I click on one of the linked pages. I've added this code in Code Injection, and while the linked pages underline as I hover over them, I want them to remain underlined for the linked page I'm actively in.

<style>
#header a:active{
 text-decoration: underline !important;
}

#header a:hover{
 text-decoration: underline !important;
}

div.folder.active{
 text-decoration: underline !important;
}

</style>

Thanks!

Link to your page please.