Find closest value in range

[minxe]

My code loops through lots of blocks of data that are separated with a 'd' (see attachment).

The code loops through each block of data between the d's perfectly.

But I can't get it to search each block - the code in red won't work no matter how I change it.

What it should do is search the values in column D and find the one that's closest to the value in column N. Once it's done that, an X should appear in the same row in Column F - as per the bottom 2.

My code is here:

Sub subd()

    Columns("F:N").Select
    Selection.ClearContents
  
    Dim rngFind As Range
    Dim strValueToPick As String
    Dim rngLook As Range
    Dim strFirstAddress As String
    Dim topRow As Long
    Dim botRow As Long
    Dim count As Integer
    Dim W As Integer
    
    Set rngLook = Range("B1:B" & Cells(Rows.count, "B").End(xlUp).Row)
    strValueToPick = "d"
    With rngLook
        Set rngFind = .Find(strValueToPick, LookIn:=xlValues, LookAt:=xlWhole)
        If Not rngFind Is Nothing Then
            strFirstAddress = rngFind.Address
            Do
                topRow = rngFind.Row
                Set rngFind = .FindNext(rngFind)
                botRow = rngFind.Row - 1
                If botRow - topRow > 1 Then

count = botRow - topRow
W = (count * (Range("D" & topRow + 1).Value)) / WorksheetFunction.Pi
Range("D" & topRow + 1).Offset(0, 10).Value = W


If Range("D" & topRow + 1).Offset(3, 0).Value < 20 Then

' +++++++++++++++++++++++++

    Dim d As Double, i As Long, j As Long
    Dim LR As Long, x
    d = 1000
    LR = botRow - topRow
    
    x = Range("D" & topRow + 1).Offset(0, 10).Value

    For i = 1 To LR + 1
        If Range("D" & i).Value = "" Then
            d = 1000
            x = Range("N" & i + 1).Value
            Range("f" & j).Value = "X"
        Else
            If Abs(Range("D" & i).Value - x) < d Then
                j = i
                d = Abs(Range("D" & i).Value - x)
            End If
        End If
    Next i

' +++++++++++++++++++++++++

Else
Range("D" & topRow + 1).Offset(2, 2).Value = "b1"
End If
        End If
            Loop While Not rngFind Is Nothing And rngFind.Address <> strFirstAddress
        End If
    End With

End Sub