如何在CSS中制作带有搜索和关闭图标的动画搜索框？

<div class="search-box">
  <input type="text" class="search-input" placeholder="搜索">
  <button class="search-btn">
    <i class="fa fa-search"></i>
  </button>
  <button class="close-btn">
    <i class="fa fa-times"></i>
  </button>
</div>

.search-box {
  position: relative;
  display: inline-block;
}

.search-input {
  width: 200px;
  padding: 8px;
  border: none;
  border-radius: 20px;
  outline: none;
  transition: width 0.3s ease-in-out;
}

.search-btn,
.close-btn {
  position: absolute;
  top: 50%;
  transform: translateY(-50%);
  background: none;
  border: none;
  cursor: pointer;
}

.search-btn {
  right: 40px;
}

.close-btn {
  right: 10px;
  opacity: 0;
  transition: opacity 0.3s ease-in-out;
}

.fa {
  font-size: 16px;
}

.fa-search:before {
  content: "\f002";
}

.fa-times:before {
  content: "\f00d";
}

.search-input:focus {
  width: 300px;
}

.search-input:focus + .search-btn {
  opacity: 0;
}

.search-input:focus + .close-btn {
  opacity: 1;
}

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">