make margins on content and block 5px instead of 10px

This decreases the amount of wasted border space
attempt to stop blocks from spilling offscreen in handheld view

And to keep the blocks width matching the contents, but I failed to do
that, the styles get a bit complicated.  It's acceptable, but I may
revisit this later.  The problem is visible when viewing the page in a
small window, like a phone.  The blocks are narrower than the content.
They should match.  However, the responsive stylesheets apply a 100% o
the second sidebard blocks which makes it expand too much; then there
is something else (I forget what) which makes the blocks too narrow.