Here is what is in Help for Excel. Are you trying to angle the borders
without angling the text because the following method slants both text
and borders?
APPLY ANGLED TEXT AND BORDERS
1. Select the cells you want to format.
2. On the *Format* menu, click *Cells*.
3. On the *Border* tab, apply vertical borders to the left, right, and
middle of the range.
4. On the *Alignment* tab, in the *Orientation* box, click a degree
point, or drag the indicator to the angle you want.
*Note* It's usually best to select a positive angle between 30 and 60
degrees.
5. Under *Text alignment*, in the *Horizontal* list box, click
*Center*, and then click *OK*.
Excel rotates the left and right borders along with the text.
6. To shrink all the columns to their smallest possible width, select
them, point to *Column* On the *Format* menu, and then click *AutoFit
Selection*.