html, body {
  height: 1000px;
}
body, p {
  margin: 0;
}
.container {
  width: 600px;
  margin: auto;
  margin-top: 100px;
}

.content {
  float: left;
  position: relative;
  height: 150px;
  width: 150px;
  margin: 20px;
  overflow: hidden;
  background: #ccc;
}

.content .shade {
  position: absolute;
  top: 0;
  display: none;
  width: 100%;
  height: 100%;
  line-height: 150px;
  color: #fff;
  text-align: center;
  background: rgba(0, 0, 0, 0.2);
}