.a {
  position: absolute;
  left: 0px;
  top: 0px;
  z-index: -1;
}
body{background-color: lightblue;
}

ul {
background-color: #f1f1f1;
  width: 50%;
  margin: 10px;
  text-align: center;
  line-height: 75px;
  font-size: 30px;
}

li {
  float: none;
}

li a {
      display: flex;
  flex-wrap: nowrap;
  background-color: white;
  color: black;
  text-align: center;
  padding: 14px 16px;
  text-decoration: none;

}

li a:hover {
  background-color: #8c4843;
  color:white;
}




.container {
  position: relative;
  width: 20%;
  background-color: gray;
  border: 15px solid black;
  padding: 15px;
  margin: 20px;
  border-radius: 30px;
  float:left;
}
.container2 {
  position: relative;
  width: 20%;
  background-color: gray;
  border: 15px solid black;
  padding: 15px;
  margin: 20px;
  border-radius: 30px;
  float:left;
}

.kuva {
  opacity: 0.3;
  display: block;
  width: 100%;
  height: auto;
  transition: .5s ease;
  backface-visibility: hidden;
}
.middle {
  transition: .5s ease;
  opacity: 0;
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(50%, 50%);
}
.kuva2 {
  opacity: 1;
  display: block;
  width: 100%;
  height: auto;
  transition: .5s ease;
  backface-visibility: hidden;
}

.middle2 {
  transition: .5s ease;
  opacity: 1;
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}
.container2:hover .kuva2 {
  opacity: 0.3;
}
.container2:hover .middle2 {
  opacity: 0.3;
}

.container:hover .kuva {
  opacity: 1;
}

.container:hover .middle {
  opacity: 1;
}
.overlay {
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  background-color: #000000;
  overflow: hidden;
  width: 0;
  height: 100%;
  transition: .5s ease;
}

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