You don't. The dialog displayed via MsgBox
uses the font that is configured for system dialogs. If you need a custom dialog you need to build a custom dialog, e.g. like this:
Sub CustomMsgBox(msg)
Set ie = CreateObject("InternetExplorer.Application")
ie.Navigate "about:blank"
While ie.ReadyState <> 4 : WScript.Sleep 100 : Wend
ie.ToolBar = False
ie.StatusBar = False
ie.Width = 300
ie.Height = 120
ie.document.body.innerHTML = "<p class='msg'>" & msg & "</p>" & _
"<p class='ctrl'><input type='hidden' id='OK' name='OK' value='0'>" & _
"<input type='submit' value='OK' id='OKButton' " &_
"onclick='document.all.OK.value=1'></p>"
Set style = ie.document.CreateStyleSheet
style.AddRule "p.msg", "font-family:times new roman;font-weight:bold;"
style.AddRule "p.ctrl", "text-align:rightf;"
ie.Visible = True
On Error Resume Next
Do While ie.Document.all.OK.value = 0
WScript.Sleep 200
Loop
ie.Quit
End Sub
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