You are correct that body form
would take precedence over form
, but the problem is in the border declaration. When specifying the values for the border property you should also include the borders width and color as well as the style.
border: double 3px #000;
this would set the elements border to the style of double, a width of 3px, and a color of black.
Make a note that when using border-style double the minimum border-width to make both borders visible is 3px.
Here is a example.