[css] How to make shadow on border-bottom?

funny, that in the most answer you create a box with the text (or object), instead of it create the text (or object) div and under that a box with 100% width (or at least what it should) and with height what equal with your "border" px... So, i think this is the most simple and perfect answer:

<h3>Your Text</h3><div class="border-shadow"></div>

and the css:

    .shadow {
        width:100%;
        height:1px; // = "border height (without the shadow)!"
        background:#000; // = "border color!"
        -webkit-box-shadow: 0px 1px 8px 1px rgba(0,0,0,1); // rbg = "border shadow color!"
        -moz-box-shadow: 0px 1px 8px 1px rgba(0,0,0,1); // rbg = "border shadow color!"
        box-shadow: 0px 1px 8px 1px rgba(0,0,0,1); // rbg = "border shadow color!"

}

Here you can experiment with the radius, etc. easy: https://www.cssmatic.com/box-shadow