How to change height of class in edit mode

i am trying to change the style of my css class in edit mode but nothing happens here is my code

<Publishing:EditModePanel runat="server" id="editmodestyles">

$(.center).css('height', '300px');

    <SharePoint:CssRegistration ID="CssRegistration1" name="&lt;% $SPUrl:~sitecollection/Style Library/~language/Themable/Core Styles/editmode15.css %&gt;" After="&lt;% $SPUrl:~sitecollection/Style Library/~language/Themable/Core Styles/pagelayouts15.css %&gt;" runat="server">
    </SharePoint:CssRegistration>

</Publishing:EditModePanel>