jQuery addClass example

Change class name on click in jQuery

HTML

<div class="wrapper">
  <div class="sec" id="section-1">section-1</div>
  <div class="sec" id="section-2">section-2</div>
  <div class="blog">
    <p>Blog</p>
  </div>
  <h1>Заголовок</h1>
</div>

CSS

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
.wrapper {
  display: flex;
  flex-direction: column;
  position: relative;
}

.sec {
  width: 100%;
  height: 400px;
}
#section-1 {
  background: #ccc;
}
#section-2 {
  background: #eee;
  position: relative;
}
h1 {
  position: absolute;
  left: 50%;
  transform: translateX(-50%);
  bottom: 30px;
}
.blog {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  width: 50%;
  height: 50%;
  border: 1px solid black;
  display: flex;
  justify-content: center;
  align-items: center;
  text-transform: uppercase;
  font-size: 40px;
  background: #fff;
}