.sidebar_classname wordpress

Good morning,

Where I found the “.sidebar_classname”?

I insert the code, but don’t work:

.sidebar_classname div.easy-instagram-thumbnail-wrapper img.easy-instagram-thumbnail{
width:200px !important;
height:auto !important;
}

I need replace “.sidebar_classname” for what?

Tks!

http://ww.wp.xz.cn/extend/plugins/easy-instagram/