How do I combine 2 (or more) styles in a cricheditctrl

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C++

MFC

RichTextBox

I was trying to combine different styles in a CRichEditCtrl control but couldn't find out how.
My goal:
to send this string "Normal text:\n```some code```\nMore text\n" and have the 'some code' part shown differently.

What I have tried:

I tried the following but the text looks the same.

DWORD CALLBACK EditStreamCallback(DWORD_PTR dwCookie, LPBYTE pbBuff, LONG cb, LONG* pcb)
{
    CString* pStr = reinterpret_cast<CString*>(dwCookie);
    *pcb = pStr->GetLength() * sizeof(TCHAR);
    memcpy(pbBuff, pStr->GetBuffer(), *pcb);
    return 0;
}


void myDialog::ApplySourceCodeStyleToText(CRichEditCtrl& m_editControl)
{
    // Get the current text in the CRichEditCtrl control
    CString text;
    m_editControl.GetWindowTextW(text);

    // Find the starting and ending positions of the code portion
    int startPos = text.Find(L"```");  // Prefix with L to create wide-character string
    int endPos = text.Find(L"```", startPos + 3);  // Prefix with L to create wide-character string

    if (startPos != -1 && endPos != -1 && endPos > startPos)
    {
        // Get the code portion from the text
        CString code = text.Mid(startPos + 3, endPos - startPos - 3);

        // Define the RTF string for the source code style
        CString rtfSourceCodeStyle = L"{\\rtf1\\ansi\\deff0{\\colortbl;\\red0\\green0\\blue255;}{\\f1\\fs20\\cf1 ";
        CString rtfEnd = L"}}";

        // Combine the RTF-formatted code with the surrounding text
        CString rtfText;
        rtfText.Format(L"%s%s%s", text.Left(startPos + 3), rtfSourceCodeStyle, code);
        rtfText.AppendFormat(L"%s%s", rtfEnd, text.Mid(endPos));

        // Convert the RTF text to plain text
        CString plainText;
        EDITSTREAM es;
        es.dwCookie = reinterpret_cast<DWORD_PTR>(&plainText);
        es.pfnCallback = EditStreamCallback;
        m_editControl.StreamIn(SF_TEXT, es);

        // Set the new text with source code style
        m_editControl.SetWindowTextW(rtfText);

        // Convert the plain text to RTF and set the selection
        m_editControl.SetSel(0, -1);
        m_editControl.ReplaceSel(plainText, TRUE);
        m_editControl.SetSel(-1, 0);
    }
}