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Option Explicit
'------------------------------------------------------
Sub encadrer()
Dim Derlig As Integer, Dercol As Byte
Dim Nbre As Integer, Cptr As Integer, Lig As Integer, Col As Byte

    Application.ScreenUpdating = False

    '--------------------------bordures horizontales
    'bas du cadre
    Derlig = Columns("A").Find(what:="*", searchdirection:=xlPrevious).Row + 1
    Range(Cells(Derlig, "A"), Cells(Derlig, "O")).Borders(xlEdgeBottom).Weight = xlMedium
    'lignes intermédiaires
    Nbre = Application.CountIf(Columns("A"), "*")
    Lig = 5
    For Cptr = 1 To Nbre
        Lig = Columns("A").Find(what:="*", After:=Cells(Lig, "A")).Row
        If Cells(Lig, "A").Interior.ColorIndex = 8 Then _
                Range(Cells(Lig, "A"), Cells(Lig, "O")).Borders(xlEdgeTop).Weight = xlMedium
    Next

    '-------------------------bordures verticales
    'droite du cadre
    Dercol = Rows(5).Find(what:="*", searchdirection:=xlPrevious).Column
    Range("O5:O" & Derlig).Borders(xlEdgeRight).Weight = xlMedium
    'colonnes intermédiaires
    Nbre = Application.CountA(Rows(5)) - 1
    Col = 1
    For Cptr = 1 To Nbre
        Col = Rows(5).Find(what:="*", After:=Cells(5, Col)).Column
        Range(Cells(5, Col), Cells(Derlig, Col)).Borders(xlEdgeLeft).Weight = xlMedium
    Next
End Sub