A user style for displaying a drop shadow under the address bar of any browser.

address-bar-drop-shadow.user.css

/* ==UserStyle==
@name        Address bar drop shadow
@description Displaying a drop shadow under the address bar of any browser.
@author      Hazem AbuMostafa (http://hazemam.com)
@homepageURL https://gist.github.com/HazemAM/86dfaa3f34c197c75a403af315c806a1
@updateURL   https://gist.github.com/HazemAM/86dfaa3f34c197c75a403af315c806a1/raw/address-bar-drop-shadow.user.css
@namespace   github.com/hazemam
@version     1.0.6
@license     Apache-2.0
==/UserStyle== */

html:not([stylus-iframe]):before {
    content: '';
    
    width: 100%;
    height: 10px;
    position: fixed;
    z-index: 9999999;
    top: 0;
    
    pointer-events: none;
    
    background: linear-gradient(to bottom, rgba(0,0,0,0.075) 2px, transparent 2px),	
                linear-gradient(to bottom, rgba(0,0,0,0.075), transparent);
}