JSFiddle - React, Tailwind, and code Playground

HTML

<p>how to remove the top border?</p><br/>
<div class="old"> something </div>

<div class="removeTopBorder"> new </div>

CSS

body {
    background-color: #000;
}
div.old {
    margin-top: 25px;
    color: #fff;
    height: 45px;
    margin-top: -5px;
    z-index: -10;
    padding: 26px 24px 46px;
    font-weight: normal;
    background: #000; /*#fff;*/
    border-top: 0px solid #e5e5e5;
    border-left: 1px solid #e5e5e5;
    border-right: 1px solid #e5e5e5;
    border-bottom: 1px solid #e5e5e5;
    -webkit-border-radius: 3px;
    -khtml-border-radius: 3px;
    -moz-border-radius: 3px;
    border-radius: 3px;
    -webkit-box-shadow: rgba(200,200,200,0.7) 0px 0px 10px 0px;
    -khtml-box-shadow: rgba(200,200,200,0.7) 0px 0px 10px 0px;
    -moz-box-shadow: rgba(200,200,200,0.7) 0px 0px 10px 0px;
    box-shadow: rgba(200,200,200,0.7) 0px 0px 10px 0px;
}
p {
    color: #fff;
}

div.removeTopBorder {
    margin-top: 25px;
    color: #fff;
    height: 45px;


    padding: 26px 24px 46px;

    

    border-left: 1px solid #e5e5e5;
    border-right: 1px solid #e5e5e5;
    border-bottom: 1px solid #e5e5e5;
    border-top: none;
    
    -moz-box-shadow: 0 0 10px 1px black,  0px -20px black, 0px 1px 10px rgba(255,255,255,0.7);
    -webkit-box-shadow: 0 0 10px 1px black,  0px -20px black, 0px 1px 10px rgba(255,255,255,0.7);
    box-shadow: 0 0 10px 1px black,  0px -20px black, 0px 1px 10px rgba(255,255,255,0.7);
    
}