<div class="container">
  <div class="content">
    <h2>web前端开发</h2>
    <p>我的github首页:https://github.com/mankeung</p>
  </div>
  <div class="toggleBtn"></div>
</div>

*{
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: 'Poppins', sans-serif;
}
body 
{
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  background: #1a242a;
}
.container 
{
  position: relative;
  width: 0px;
  height: 0px;
  background: #37444b;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 25px;
  transition: 0.5s;
}
.container::before 
{
  content: '';
  position: absolute;
  bottom: -15px;
  width: 40px;
  height: 40px;
  background: #37444b;
  border-radius: 5px;
  opacity: 0;
  transform: rotate(45deg);
  transition: 0.5s;
}
.container.active::before 
{
  opacity: 1;
  transition-delay: 0.5s;
}
.container.active 
{
  width: 400px;
  height: 400px;
  transition-delay: 0.5s;
}
.container .content 
{
  min-width: 400px;
  padding: 40px;
  color: #fff;
  opacity: 0;
  transition: 0.5s;
  transform: scale(0);
}
.container.active .content 
{
  opacity: 1;
  transition-delay: 0.5s;
  transform: scale(1);
}
.toggleBtn 
{
  position: absolute;
  bottom: -20px;
  min-width: 60px;
  height: 60px;
  background: #0bcf9c;
  border-radius: 50%;
  cursor: pointer;
  display: flex;
  justify-content: center;
  align-items: center;
  transition: 0.5s;
}
.container.active .toggleBtn 
{
  bottom: -90px;
  transform: rotate(135deg);
  background: #ff5a57;
}
.toggleBtn::before 
{
  content: '+';
  font-size: 2.5em;
  color: #fff;
}

let toggleBtn = document.querySelector('.toggleBtn');
let container = document.querySelector('.container');
toggleBtn.onclick = function(){
  container.classList.toggle('active');
}