following scroll button css(essence)

following-scroll-button.css

.followcard {
	position: fixed;
	top: -2000px;

	z-index: 999;
        margin-left:16px; 
	padding:10px;
	background:#7777ff;
	border-radius: 8px;
    
        visibility: visible;
}
input#start:checked + .followcard{
            background:#77f;
            top: -webkit-calc(90vh - 20px);
            top: -moz-calc(90vh - 20px);
            top: calc(90vh - 20px);
            left:90vw;
            cursor:pointer;
}
.flow input{
            display:none;
}

following-scroll-button.html

<div class="flow">
    <input type="radio" name="status" id="start" checked="checked">
    <div class="followcard">
        
         <label for="close">X close</label>
    </div>
    <input type="radio" name="status" id="close">
</div>

explain & moving sample
http://edutainment-fun.com/hidemaru/it/css%E3%81%A0%E3%81%91%E3%81%A7%E8%BF%BD%E5%BE%93%E3%81%99%E3%82%8B%E3%83%9C%E3%82%BF%E3%83%B3%E3%82%92%E5%AE%9F%E8%A3%85%E3%81%97%E3%81%A6%E3%81%BF%E3%81%9F_2479.html