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 Make a new file that is a square. 
Choose a light/bright color for the 1st color and then choose 
a darker color for the 2nd color. Use the    gradient tool  
and fill the image diagonally from dark to the light colors from the corners.
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 Select all (CTRL A) and click Select>Modify>Border. 
Type in any number 1 - 5 (This example is 4). 
Now fill the selection with the same colors from before but change the direction. | 
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 The last step is to type any word on the button that you want, and there you have it, a beveled 3D button. |