Javascript example

HTML

<div id="popUpDiv" class="popup" style="background: red; border-color: red;">
    <p>University</p>
<button onclick="myFunction()">CLOSE</button>
</div>

CSS

.popup {
    padding: 25px;
    position: relative;
    width:'100%';
    
}
.popup:after {
    content: "x";
    position: absolute;
   top: 80%;
   left: 20px;
   border-top: 20px solid blue;
   border-top-color: inherit; 
   border-left: 20px solid transparent;
   border-right: 20px solid transparent; 
}

JavaScript

function myFunction()
{
document.getElementById("popUpDiv").style.display = "none";
}