Full Screen Search Box HTML

 HTML CODE

<div id="myOverlay" class="overlay">

  <span class="closebtn" onclick="closeSearch()" title="Close Overlay">x</span>
  <div class="overlay-content">
    <form action="action_page.php">
      <input type="text" placeholder="Search.." name="search">
      <button type="submit"><i class="fa fa-search"></i></button>
    </form>
  </div>
</div>

CSS CODE

/* The overlay effect with black background */
.overlay {
  height: 100%;
  width: 100%;
  display: none;
  position: fixed;
  z-index: 1;
  top: 0;
  left: 0;
  background-color: rgb(0,0,0);
  background-color: rgba(0,0,0, 0.9); /* Black with a little bit see-through */
}

/* The content */
.overlay-content {
  position: relative;
  top: 46%;
  width: 80%;
  text-align: center;
  margin-top: 30px;
  margin: auto;
}

/* Close button */
.overlay .closebtn {
  position: absolute;
  top: 20px;
  right: 45px;
  font-size: 60px;
  cursor: pointer;
  color: white;
}

.overlay .closebtn:hover {
  color: #ccc;
}

/* Style the search field */
.overlay input[type=text] {
  padding: 15px;
  font-size: 17px;
  border: none;
  float: left;
  width: 80%;
  background: white;
}

.overlay input[type=text]:hover {
  background: #f1f1f1;
}

/* Style the submit button */
.overlay button {
  float: left;
  width: 20%;
  padding: 15px;
  background: #ddd;
  font-size: 17px;
  border: none;
  cursor: pointer;
}

.overlay button:hover {
  background: #bbb;

}

 JS CODE

// Open the full screen search box
function openSearch() {
  document.getElementById("myOverlay").style.display = "block";
}

// Close the full screen search box
function closeSearch() {
  document.getElementById("myOverlay").style.display = "none";
}