Editing bottom border on pagelayer menu

I am struggling to find where and how to edit the orange bottom border of the current page of the desktop nav menu. I have found the code

.p-c0l273 .pagelayer-wp-menu-container .current-menu-item a {
font-size: 140% !important;
border-bottom: 2px solid #eeaa6d;
}

but as to where to find that in the theme files to edit I am stumped.

Any help would be appreciated

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