Sub Marquer_Doublons()
Dim rng As Range
Set rng = Range([D4], Cells(Rows.Count, "D").End(3))
rng.FormatConditions.AddUniqueValues
rng.FormatConditions(rng.FormatConditions.Count).SetFirstPriority
With rng.FormatConditions(1)
.DupeUnique = xlDuplicate
.Borders.LineStyle = 1
.Borders.Color = vbRed
.Interior.Color = vbYellow
.Font.Color = vbRed
.Font.Bold = True
End With
End Sub