ブートストラップ3の要素を折りたたむためにYスクロールバーを追加できない

Question

このデモを見て、ブートストラップ3のcollapse in要素内の.wellにYスクロールバーを追加できない理由を教えてください。

@import url('https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css'); 
 
.well{ 
 
     height: 120px !important; 
 
     max-height: 120px !important; 
 
     overflow-y: visible; 
 
    }

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> 
 
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script> 
 
<div class="container"> 
 
    <a class="btn btn-primary" role="button" data-toggle="collapse" href="#collapseExample" aria-expanded="false" aria-controls="collapseExample"> 
 
    Show Scroolbar 
 
</a> 
 
<br /> 
 
<br /> 
 
<div class="collapse" id="collapseExample"> 
 
    <div class="well"> 
 
    <p>Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.</p> 
 
    <p>Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.</p> 
 
    </div> 
 
</div> 
 
    
 
</div>

おかげ

Answer 1

ただオーバーフロー-yのプロパティを変更し、高さプロパティを削除します。

@import url('https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css'); 
 
.well{ 
 
     max-height: 120px !important; 
 
     overflow-y: auto; 
 
    }

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> 
 
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script> 
 
<div class="container"> 
 
    <a class="btn btn-primary" role="button" data-toggle="collapse" href="#collapseExample" aria-expanded="false" aria-controls="collapseExample"> 
 
    Show Scroolbar 
 
</a> 
 
<br /> 
 
<br /> 
 
<div class="collapse" id="collapseExample"> 
 
    <div class="well"> 
 
    <p>Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.</p> 
 
    <p>Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.</p> 
 
    </div> 
 
</div> 
 
    
 
</div>