• Now Time for giving the Slide effects, Add the Code ABOVE the Popular posts widget, Go to Blogger > Layout > Add a Gadget > Html/Javascript.  Paste the Below Code.

Keep both Widgets together, like the image.

<style type="text/css" media="screen">
#PopularPosts1 {
overflow:hidden;
margin-top:5px;
width:100%;
padding:0px 0px;
height:310px;
}
#PopularPosts1 ul {
width:310px;
overflow:hidden;
list-style-type: none;
padding: 0px 0px;
margin:10px 0px 0px 10px;
}
#PopularPosts1 li {
 width:290px;
padding: 5px 5px;
margin:0px 0px 5px 0px;
list-style-type:none;
float:none;
height:80px;
overflow: hidden;
background:#fff url(https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEguU5G0QYm8KpfecW2kkpHY_l_ZJrZ8yXCSKQtlsuOS3rGt46_bKx0uIYUFDpAMFxW_b-IVGVGnFzNUea827gcSrfsEsA91OS2bE7xkuU_hJXu8oiE_hZfI3rTk_lbfPtzk6Ih5RhvMvMY/s400/popular+posts.jpg) repeat-x;
border:1px solid #ddd;
}
#PopularPosts1 li .item-title {
  
    font-size:1em;
    margin-bottom:0.5em;
}
#PopularPosts1 li .item-title a {
text-decoration:none;
color:#7CA2C4; font:bold 12px verdana; 
height:18px;
overflow:hidden;
margin:0px 0px;
padding:0px 0px 2px 0px;
}
#PopularPosts1 li img {
float:left;
margin-right:5px;
background:#EFEFEF;
border:2px solid #7CA2C4; 
}
#PopularPosts1 li .item-snippet {   overflow:hidden; font-family:Tahoma,Arial,verdana, sans-serif; font-size:10px; color:#289728; padding:0px 0px; margin:0px 0px; }#PopularPosts1 .item-snippet a,
#PopularPosts1 .item-snippet a:visited {
    color:#3E4548;
    text-decoration: none;
}
#PopularPosts1 .spyWrapper {
    height: 100%;
    overflow: hidden;
    position: relative;
}
#PopularPosts1 {
    -webkit-border-radius: 5px;
    -moz-border-radius: 5px;
}
.tags span,
.tags a {
    -webkit-border-radius: 8px;
    -moz-border-radius: 8px;
}
a img {
    border: 0;
}
-->
</style>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js"type="text/javascript"></script>
<script type="text/javascript" charset="utf-8">
$(function () {
    $('.popular-posts ul').simpleSpy();
});
</script>
<script src="http://accordion-for-blogger.googlecode.com/svn/trunk/simplespy.js"type="text/javascript"></script>

• You can Change Widget container height by editing height:310px;
• To change the small rectangles width edit width:310px
• If you want to change the width of the text snippet then edit width:290px;. Keep this width 20px smaller than the rectangles width. For example in this widget I have kept rectangles width=310px; and snippet width=290px;
• easily change the link title color and font size edit color:#7CA2C4; font:bold 12px verdana;

• You can change the thumbnail image's border colour and size by editing border:2px solid #7CA2C4
• To change the snippet text's font size, family and colour then edit the yellow highlighted code