1.Login to your blogger dashboard--> layout- -> Edit HTML

2.Scroll down to where you see </head> tag .

3.Copy below code and paste it just before the </head> tag .

<style type='text/css'>
#search {
height:34px;
width:auto;
margin-top:10px;
padding:17px 5px 10px 15px;
width:311px;
background:url(http://3.bp.blogspot.com/_4HKUHirY_2U/SwN64d149xI/AAAAAAAAAM8/8HfSzziMgfs/search.png);
}
#search form {
margin: 0;
padding: 0;
}

#search fieldset {
margin: 0;
padding: 0;
border: none;
}

#search p {
margin: 0;
font-size: 85%;
}

#s {
margin-left:0px;
float: left;
width:231px;
padding: 6px 2px 6px 5px;
background:#fff url(http://3.bp.blogspot.com/_4HKUHirY_2U/SwN7CyGqi2I/AAAAAAAAANM/SkrrbPdThGU/s1600/sform.png) no-repeat;
border:none;
font: normal 100% &quot;Tahoma&quot;, Arial, Helvetica, sans-serif;
color:#C6C6C6;
}

#searchsubmit {
width:57px;
float: left;
background:#fff url(http://2.bp.blogspot.com/_4HKUHirY_2U/SwN68gRqCFI/AAAAAAAAANE/HYdbueuk378/sbutton.png);
border:none;
font: bold 100% &quot;century gothic&quot;, Arial, Helvetica, sans-serif;
color: #FFFFFF;
height:28px;
margin-left:5px;
}

</style>

Note:Please host above 3 images yourself.

4.Now save your template.

5.Go to Layout-->Page Elements and click on "Add a gadget".

6.Select "html/java script" and add the code given below and click save.

<div id='search'>
<form id="searchform" action="http://YOURBLOG.blogspot.com/search" style="display:inline;" method="get">
<input id="s" name="q" type="text" value=""/>
<input id="searchsubmit" value="" type="submit"/>
</form>
</div>

Note: Remember to replace "YOURBLOG" with your blog name.

You are done.It will look like this:

Smart CSS Search Box to Blog/Website