jQuery addClass example

Change class name on click in jQuery

HTML

<div class="wrapper">
  <div class="box box-1">1</div>
  <div class="box box-2">2</div>
  <div class="box box-3">3</div>
</div>

CSS

* {
  margin: 0;
  padding: 0;
  -webkit-box-sizing: border-box;
  -moz-box-sizing: border-box;
  box-sizing: border-box;
}
.wrapper {
  position: relative;
}
.box {
  width: 70%;
  height: 100px;
  background: blue;
  outline: 3px solid black;
  color: #fff;
  font-size: 50px;
}

.box-2 {
  width: 29%;
  height: 200px;
  position: absolute;
  right: 0;
  top: 0;
  background: lightblue;
}

@media screen and (max-width: 540px) {
  .box {
    width: 100%;
    height: 100px;
  }
  .box-2 {
    position: static;
  }
}