.session-expired {
position: fixed;
display: block;
top: 0px;
left: 0px;
width: 100%;
height: 100%;
background-color:rgba(0, 0, 0, 0.6);
z-index: 1000;
}

.session-expired span {
position: absolute;
display: block;
top: 50%;
left: calc(50% - 140px);
width: 280px;
background-color: #fff;
color: #333;
padding: 50px;
border-radius: 10px;
text-align: center;
}