.thumbnailx1 {
  position: relative;
  display: inline-block;
}
#coverimg {
width: 100%;
height: 50vh;
background: url("n2a2NewBldg2.png") center;
background-size: cover;
position: relative;
}

#coverimg:before {
content: "";
background: rgba(0, 0, 0, 0.4);
position: absolute;
bottom: 0;
top: 0;
left: 0;
right: 0;
}
.caption1 {
  position: absolute;
  top: 50%;
  left: 40%;
  transform: translate( -50%, -50% );
  color: rgb(255, 255, 255);
  font-weight: bold;
}