lucy24 - 3:45 am on Jan 2, 2013 (gmt 0)
Border at the bottom should expand according to box around H3 not text limitation of H4.
Is there more than one h4 involved? Or rather: are there more h4s than h3s? It kinda sounds as if what you want is not a separate h4 at all, but something like <span class = "subhead"> attached to the preceding h3. The padding and border will then be properties of the h3, while the subhead only carries those properties that are different from the main h3.