CSS: Image always stick to left/right

File: styles.css

<style>
.btn_right {
 width: 50px; 
 height: 112px; 
 position: fixed; 
 right: 0pt; 
 top: 62px; 
 margin: 0px; 
 display: block;
}

.btn_left {
 width: 50px; 
 height: 112px; 
 position: fixed; 
 left: 0px; 
 top: 50%; 
 margin: -45px 0px 0px; 
 cursor: pointer; 
 display: block;
}

.btn_close_right {
 display: inline-block; 
 margin-left:30px; 
 width: 20px; 
 height: 18px; 
 background: url('close_icon.png') 0px 0px no-repeat; 
 cursor:pointer;
}
</style>

File: buttons.html

<link rel="stylesheet" type="text/css" href="styles.css" />
<!-- button always stick right -->
<div class="btn_right">
 <img style="cursor:pointer;" src="btn_right.png">
 <br>
 <div class="btn_close_right"></div>
</div>

<!-- button always stick left -->
<div class="btn_left">
 <img src="btn_left.png">
 <br>
 <img src="close_icon.png">
</div>

Positioning Tutorial: http://www.barelyfitz.com/screencast/html-training/css/positioning/