Added bottom margin to #topic_header columns css

.info col had a different margin setting than the rest. This does not matter as long a you use the default css. But if you change box sizing for all elements with * { box-sizing:content-box; } the .info column of the first row after heading will be pushed to the right.

Signed-off-by: Michael 'Tekkla' Zorn <tekkla@tekkla.de>