Input

<div class="search">
  <input type="checkbox" id="trigger" class="search__checkbox" />
  <label class="search__label-init" for="trigger"></label>
  <label class="search__label-active" for="trigger"></label>
  <div class="search__border"></div>
  <input type="text" class="search__input" />
  <div class="search__close"></div>
</div>
//Автор: Nikolay Talanov. @suez

*, *:before, *:after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html, body {
  font-size: 62.5%;
  height: 100%;
}

body {
  background: #E62878;
}

.search {
  position: absolute;
  top: 50%;
  left: 50%;
  margin-left: -16rem;
  margin-top: -3rem;
  width: 32rem;
  height: 6rem;
}
.search__border {
  position: absolute;
  top: 50%;
  left: 50%;
  width: 6rem;
  height: 100%;
  border: 0.6rem solid #fff;
  border-radius: 10rem;
  transform: translate(-50%, -50%);
  transition: width 0.4s 0.4s;
}
#trigger:checked ~ .search__border {
  transition: width 0.4s 0.2s;
  width: 100%;
}
#trigger:checked ~ .search__border:after {
  width: 0;
  transition: width 0.2s cubic-bezier(0.42, -0.7, 0.62, 1.25);
}
.search__border:after {
  content: "";
  position: absolute;
  bottom: -1.6rem;
  right: -1.6rem;
  width: 3rem;
  height: 0.6rem;
  background: #fff;
  border-radius: 0.6rem;
  transform-origin: 100% 50%;
  transform: rotate(225deg) translateX(3rem);
  transition: width 0.2s 0.8s;
}
.search__input {
  position: relative;
  width: 26rem;
  height: 6rem;
  padding: 0.9rem 0 0.9rem 2.4rem;
  background: transparent;
  outline: none;
  border: none;
  font-size: 2.4rem;
  color: #fff;
  z-index: -1;
  opacity: 0;
  transition: opacity 0.2s;
}
#trigger:checked ~ .search__input {
  opacity: 1;
  z-index: auto;
  transition: opacity 0.2s 0.6s;
}
.search__checkbox {
  position: absolute;
  top: -9999px;
  left: -9999px;
  opacity: 0;
  z-index: -10;
}
.search__label-init {
  z-index: 2;
  position: absolute;
  top: 0;
  left: 13.12rem;
  width: 6.8rem;
  height: 6.4rem;
  cursor: pointer;
}
#trigger:checked ~ .search__label-init {
  transform: scale(0);
}
.search__label-active {
  z-index: 3;
  position: absolute;
  top: 1.5rem;
  right: 1.5rem;
  width: 3rem;
  height: 3rem;
  cursor: pointer;
  transform: scale(0);
}
#trigger:checked ~ .search__label-active {
  tranition: transform 0 0.6s;
  transform: scale(1);
}
.search__close {
  position: absolute;
  top: 1.5rem;
  right: 1.5rem;
  width: 3rem;
  height: 3rem;
  cursor: pointer;
  z-index: -1;
}
#trigger:checked ~ .search__close {
  z-index: auto;
}
#trigger:checked ~ .search__close:before {
  transform: rotate(-45deg);
  opacity: 1;
  transition: transform 0.2s 0.6s cubic-bezier(0.73, 0.14, 0.4, 1.58), opacity 0.1s 0.6s;
}
#trigger:checked ~ .search__close:after {
  transform: rotate(45deg);
  opacity: 1;
  transition: transform 0.2s 0.8s cubic-bezier(0.73, 0.14, 0.4, 1.58), opacity 0.1s 0.8s;
}
.search__close:before, .search__close:after {
  content: "";
  position: absolute;
  top: 1.2rem;
  left: 0;
  width: 100%;
  height: 0.6rem;
  background: #fff;
  border-radius: 0.5rem;
  opacity: 0;
}
.search__close:before {
  transform: rotate(-45deg) translateX(2rem);
  transition: transform 0.2s, opacity 0.1s 0.1s;
}
.search__close:after {
  transform: rotate(45deg) translateX(2rem);
  transition: transform 0.2s 0.2s, opacity 0.1s 0.3s;
}