オリジナルjsを利用してカスタムスクロールバーを実現します.

1.HTMLファイル
div 1はスクロールバーで、div 2はスクロールボールで、div 3はテキストエリアの容器で、div 4はテキストエリアです.

<div id="div">
	<div id="div1">
		<div id="div2">	div>
	div>
	<div id="div3">
		<div id="div4">
			<p>CSS3   p>
			<p>CSS3   p>
			<p>CSS3   p>
			<p>CSS3   p>
			<p>CSS3   p>
			<p>CSS3   p>
			<p>CSS3   p>
			<p>CSS3     p>
			<p>CSS3   p>
			<p>CSS3 2D   p>
			<p>CSS3 3D   p>
			<p>CSS3   p>
			<p>CSS3   p>
			<p>CSS3   p>
			<p>CSS3     p>
			<p>CSS3   p>
			<p>CSS3   p>
			<p>CSS3   p>
			<p>CSS3    p>
			<p>CSS3     p>
			<p>CSS3      p>
			<p>CSS3        p>
		div>
	div>
div>

2.cssスタイルファイル
コンテナオーバーフローで隠し、テキストエリアの絶対位置をjsに渡します.

*{padding: 0; margin: 0;}
#div{top:200px;left:25%;width: 50%;height: 300px; position: absolute; 
}
#div1{width: 20px; height: 300px; position: relative; 
background: #CCCCCC; border-radius: 28px; float: right; cursor: pointer;}
#div1 #div2{left: -4px;width: 28px;height: 28px;border-radius: 50%; background: red;
position: absolute;}

#div3{width: 90%; height: 300px; border: 2px solid #CCCCCC;
position: relative; float: left; overflow: hidden;}
#div3 #div4{top:0;left:0;width: 100%; position: absolute; font-family: "    ";
font-size: 19px; letter-spacing: 1px; padding: 3px 6px;}

3.jsスクリプトコード

window.onload =function(){
	var allDiv =document.getElementById('div');
	var oDiv =document.getElementById('div2');
	var aDiv =document.getElementById('div1');
	var textDiv1 =document.getElementById('div3');
	var textDiv2 =document.getElementById('div4');
	
	//      ，        
	oDiv.onmousedown =function(ev){
		var oEvent =ev||event;
		
		var disY =oEvent.clientY -oDiv.offsetTop;
		
		if(oDiv.setCapture){
			oDiv.onmousemove =mouseMove;
			oDiv.onmouseup =mouseUp;
			
			oDiv.setCapture();
		}else{
			document.onmousemove =mouseMove;
			document.onmouseup =mouseUp;
		}
		
		function mouseMove(ev){
			var oEvent =ev||event;						
			var t =oEvent.clientY -disY;					
			var bottomLine = aDiv.offsetHeight-oDiv.offsetHeight;	
			
			
			if(t <0){
				t =0;
			}else if(t >bottomLine){
				t =bottomLine;
			}
			
	        var percent =t/272;
	        
			oDiv.style.top =t+'px';
			textDiv2.style.top =-(textDiv2.offsetHeight-textDiv1.offsetHeight)*percent+'px';
			
		};
		
		function mouseUp(){
			this.onmousemove =null;
			this.onmouseup =null;
			
			if(oDiv.releaseCapture){
				oDiv.releaseCapture();
			}
		};
	
	    return false;
	};
	
	//      ，     ，          ，     
	aDiv.onmousedown=function(ev){
		var oEvent =ev||event;					
		var divY =oEvent.clientY-allDiv.offsetTop;
		var timer =null;var speed=10;
		
		
		clearInterval(timer)
		timer = setInterval(function(){
			var percent=oDiv.offsetTop/272;
			
			
			if(oDiv.offsetTop<divY-28){
				oDiv.style.top =oDiv.offsetTop + speed +'px';
				textDiv2.style.top =-(textDiv2.offsetHeight-textDiv1.offsetHeight)*percent +'px';
			}else if(oDiv.offsetTop>divY){
				oDiv.style.top =oDiv.offsetTop - speed +'px';
				textDiv2.style.top =-(textDiv2.offsetHeight-textDiv1.offsetHeight)*percent +'px';
			}else if(oDiv.offsetTop>260){
				oDiv.offsetTop = 272+'px';
				clearInterval(timer);
			}else if(oDiv.offsetTop<10){
				oDiv.offsetTop = 0+'px';
				clearInterval(timer);
			}else{
				clearInterval(timer);
			}
			
			
		},10);
		
	}
	
	
	
}