I have a Telerik RadEditor (2017.3) control with custom/unembedded skin (created using the themebuilder on telerik), and when I enter a value for the DialogsCssFile attribute, the markup of the page changes, meaning that my custom skin is not applied to the editor anymore.

Why is this a problem? Well the css inside the dialog for Find/replace for example didn't display correct, and having done some research, I needed to do some @imports into a customDialog.css file and drop that into the DialogsCssFile attribute.

As soon as I do this, the generated markup in the page for RadEditor changes from

Radeditor RadEditor_MyCustomSkin reWrapper

to

Radeditor MyCustomSkin reWrapper

meaning that my radeditor Skin is not applied to the editor, If I remove the DialogCssFile then the editor skin loads correctly, but the dialogs look wrong. In the Page source, the Window is a div within the page, and not an iFrame

Code :

Page CSS files (in order)

<link type="text/css" rel="stylesheet" href="/assets/css/MyCustomSkin/formdecorator.MyCustomSkin.css" />
<link type="text/css" rel="stylesheet" href="/assets/css/MyCustomSkin/toolbar.MyCustomSkin.css" />
<link type="text/css" rel="stylesheet" href="/assets/css/MyCustomSkin/window.MyCustomSkin.css" />
<link type="text/css" rel="stylesheet" href="/assets/css/MyCustomSkin/combobox.MyCustomSkin.css" />
<link type="text/css" rel="stylesheet" href="/assets/css/MyCustomSkin/dropdownlist.MyCustomSkin.css" />
<link type="text/css" rel="stylesheet" href="/assets/css/MyCustomSkin/tabstrip.MyCustomSkin.css" />
<link type="text/css" rel="stylesheet" href="/assets/css/MyCustomSkin/editor.MyCustomSkin.css" />
Main Radeditor Class (to give idea of class names)

.RadEditor_MyCustomSkin { /* css styles - all generated automatically */ }
Control :

<telerik:RadEditor runat="server" ID="pageRadEdit" ToolbarMode="Default" EditModes="Design,Html"
DialogsCssFile="~/assets/css/MyCustomSkin/DialogHandler.MyCustomSkin.css"
ToolsFile="~/App_Data/Editor.xml" Width="980px" Height="800px"
EnableResize="false" OnClientLoad="resizeMe" NewLineMode="P"
OnClientSelectionChange="$page.setdirty"
ContentFilters="DefaultFilters,ConvertFontToSpan,IECleanAnchors,OptimizeSpans,MozEmStrong,FixEnclosingP"
EnableEmbeddedSkins="false">
        <SpellCheckSettings DictionaryLanguage="en-GB" AllowAddCustom="false" />
        <Languages>
            <telerik:SpellCheckerLanguage Code="en-GB" Title="English (UK)" />
        </Languages>
</telerik:RadEditor>
DialogHandler.MyCustomSkin.css

@import url('FormDecorator.MyCustomSkin.css');
/*@import url('Grid.MyCustomSkin.css');*/
@import url('Input.MyCustomSkin.css');
@import url('Splitter.MyCustomSkin.css');
@import url('TabStrip.MyCustomSkin.css');
@import url('ToolBar.MyCustomSkin.css');
/*@import url('Upload.MyCustomSkin.css');*/
@import url('Window.MyCustomSkin.css');
@import url('ComboBox.MyCustomSkin.css');
@import url('Button.MyCustomSkin.css');
/*@import url('Editor.MyCustomSkin.css');*/
Note : Editor css is still using wrong class even if the bottom import is uncommented

Web.Config settings

<add key="Telerik.Skin" value="MyCustomSkin" />
<add key="Telerik.ScriptManager.TelerikCdn" value="Disabled" />
<add key="Telerik.StyleSheetManager.TelerikCdn" value="Disabled" />
<add key="Telerik.Web.UI.RenderMode" value="lightweight" />
<add key="Telerik.Web.UI.EnableEmbeddedSkins" value="false" />
<add key="Telerik.EnableEmbeddedSkins" value="false" />