democss.css

.topnav {
  overflow: hidden;
  background-color: #e9e9e9;
}

/* Style the links inside the navigation bar */
.topnav a {
  float: left;
  display: block;
  color: black;
  text-align: center;
  padding: 14px 16px;
  text-decoration: none;
  font-size: 17px;
}

/* Change the color of links on hover */
.topnav a:hover {
  background-color: #ddd;
  color: black;
}

/* Style the "active" element to highlight the current page */
.topnav a.active {
  background-color: #2196F3;
  color: white;
}

/* Style the search box inside the navigation bar */
.topnav input[type=text] {
  float: right;
  padding: 6px;
  border: none;
  margin-top: 8px;
  margin-right: 16px;
  font-size: 17px;
}

/* When the screen is less than 600px wide, stack the links and the search field vertically instead of horizontally */
@media screen and (max-width: 600px) {
  .topnav a, .topnav input[type=text] {
    float: none;
    display: block;
    text-align: left;
    width: 100%;
    margin: 0;
    padding: 14px;
  }
  .topnav input[type=text] {
    border: 1px solid #ccc;
  }
}
.image {
  display: block;
  width: 100%;
  height: auto;
}

.overlay {
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  background-color: #008CBA;
  overflow: hidden;
  width: 100%;
  height: 0;
  transition: .5s ease;
}

.container:hover .overlay {
  height: 100%;
}

.text {
  color: white;
  font-size: 20px;
  position: absolute;
  top: 50%;
  left: 50%;
  -webkit-transform: translate(-50%, -50%);
  -ms-transform: translate(-50%, -50%);
  transform: translate(-50%, -50%);
  text-align: center;
}