Conditional Format Via Code For Entire Workbook

I found code that I would like to use conditional formatting code as shown here. Here is the code just in case:

Private Sub Worksheet_Change(ByVal Target As Range)
Dim icolor As Integer

If Not Intersect(Target, Range("A1:A10")) Is Nothing Then
Select Case Target
Case 1 To 5
icolor = 6
Case 6 To 10
icolor = 12
Case 11 To 15
icolor = 7
Case 16 To 20

how can I get this code to work across the entire workbook and not just for the specific worksheet? I tried pasting the code into the This Workbook under VBA Project and changing the Private to Public but no go.