How to Add Expandable Search Box in Blogger

Go To Layout

Click On Add a Gadget

Choose HTML/JavaScript

Copy the Code & Paste it Here.

<div id='wc-searchexpand1'>
         <form name='input' action='/search'  method='get' id="wc-searchexpandbox1"> 
            <input name='q' id='wc-searchexpandinput1' onblur='if (this.value == "") {this.value = "Search this site...";}' onfocus='if (this.value == "Search this site...") {this.value = ""}' type='text' value='Search this site...'/>
            <input id='wc-searchexpandsubmit1' type='submit' value='Search'/>
         </form>
      </div>

Click on Save Button, You Have Done it.