certi.css

.overlay 
{
    position: absolute;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;
    height: 100%;
    width: 100%;
    opacity: 0;
    transition: .5s ease;
    background-image: radial-gradient(circle, #15f4ee,  black);;
}
  
.card:hover .overlay 
{
opacity: 0.8;
}

.text {
color: white;
font-size: 30px;
font-weight: 700;
font-family: 'Merriweather Sans', sans-serif;
position: absolute;
top: 50%;
left: 50%;
-webkit-transform: translate(-50%, -50%);
-ms-transform: translate(-50%, -50%);
transform: translate(-50%, -50%);
text-align: center;
text-shadow: 0 0 10px #15f4ee;
}

.card:hover
{
    box-shadow: 0 2px 20px 0 inset, 0 2px 20px 0 #15f4ee;
}