<div class="first">A</div>
<div class="second">B</div>

<div class="third">C</div>
<div class="fourth">D</div>

div {
  display: flex;
  justify-content: center;
  align-items: center;
  width: 100px;
  height: 50px;
  float: left;
}

.first {
  box-sizing: border-box;
  background: blue;
}

.first:hover {
  border: 5px solid black;
}

.second {
  margin-left: 10px;
  background: red;
}

.third {
  margin-top: 10px;
  clear: left;
  background: orange;
}

.third:hover {
  box-shadow: inset 0px 0px 0px 4px black;
}

.fourth {
  margin-top: 10px;
  margin-left: 10px;
  background: purple;
}