Conditional formatting to highlight specific cells but not empty and text cells VBA - excel

Question

I have a macro which highlights cells outside a range. The only problem with it, is that it also highlights all empty cells and cells with text. Is there a way for it to ignore these?
Here is my code
Sub Highlight()
'
' Highlight good values
Application.ScreenUpdating = False
Dim ws As Worksheet
For Each ws In ActiveWorkbook.Worksheets
ws.Activate
With ActiveSheet.Rows("18:79")
.FormatConditions.Add Type:=xlCellValue, Operator:=xlNotBetween, _
Formula1:="=$C18", Formula2:="=$D18"
.FormatConditions(Selection.FormatConditions.Count).SetFirstPriority
With .FormatConditions(1).Font
.Color = -16752384
.TintAndShade = 0
End With
With .FormatConditions(1).Interior
.PatternColorIndex = xlAutomatic
.Color = 13561798
.TintAndShade = 0
End With
.FormatConditions(1).StopIfTrue = False
End With
Next ws
Application.ScreenUpdating = True
End Sub

Answer 1

You currently only have a row limitation to the range you are applying the conditional formatting to. If you want to limit the impacted range you just need to change your With to have both a Row and a Column limitation.
Update This:
With ActiveSheet.Rows("18:79")
To This:
With ActiveSheet.Range("A18:O79")
Edit
If each sheet has the SAME row range (18:79) but the columns have a VARYING range you just need to create a last column variable to create your dynamic range
Sub Highlight()
Dim ws As Worksheet, LC As Long
For Each ws In ActiveWorkbook.Worksheets
LC = ws.Cells(18, ws.Columns.Count).End(xlToLeft).Column
With ws.Range(ws.Cells(18, 1), ws.Cells(79, LC))
'Formatting goes here
End With
Next ws
End Sub