用Javascript更改CSS“.modalDialog> div {}”

Question

我有一个模态图层与CSS。当我用Javascript打开模态图层时，我想将宽度：400px改为其他任何东西。我该怎么做？

<div id="openModal" class="modalDialog"> 
<div> 
<a href="#close" title="Close" class="close">X</a> 
<video width="640" height="480" id="notes_video" controls fullscreen> 
<source src="video/Opening.webm" type="video/webm"> 
<track kind="subtitles" src="opening.vtt" srclang="de"></track> 
Your browser does not support the video tag. 
</video> 
</div> 
</div> 

CSS-代码：

.modalDialog > div { 
    width: 400px; 
} 

感谢您的帮助

Answer 1

$(".modalDialog").css("width", "10px");