Hi @Jitendra Kumar ,

You’re running into expected CKEditor behaviour, not an OutSystems bug. CKEditor is sanitising your HTML via its Advanced Content Filter (ACF) and intentionally stripping CSS, classes, and  blocks unless you explicitly allow them.

Correct approach for OutSystems templates (recommended)

OPTION 1: Move CSS out of the HTML completely 

Do NOT inject into CKEditor content. 

Instead: 

• Put all CSS in: 
  • Theme CSS 
  • Screen CSS 
  • Block CSS 
• Use class-based styling only in your HTML

Example HTML stored in CKEditor:

<div class="invoice-header"> 
     <h1>{{CustomerName}}</h1>
</div> 

And CSS (Theme / Screen):

,invoice-header {
     font-weight: bold;  
     margin-bottom: 16px;
}

This is the only fully supported approach in CKEditor 5.

OPTION 2: Allow CSS classes in CKEditor configuration

By default, CKEditor strips classes unless allowed. In OutSystems CKEditor Forge, enable Extra Allowed Content:

extraAllowedContent: '*(*)'`` 
OR
extraAllowedContent: 'div(*);span(*);p(*);table(*);tr(*);td(*)'`` 

This tells CKEditor: 

• Allow any class 
• Preserve formatting 
• Still keep filtering active

This behaviour is documented in CKEditor ACF rules.

Hope this helps.

Cheers.

Saugat