Adding some more spacing to inline <code>
Changing font size units to rem

This will prevent trouble with nested elements inheriting paretnts' em
sizes and cascacing.
As a consequence, had to change the setting for the root font size.
Keeping that at 10px for easier mathematics.
Explicitly aligning main content from the left

Internet Explorer 11 apparently didn't get this otherwise and was
calculating the margin from the right boundary of the sidebar.
Fixing tiny difference in overlap

The idea was for the picture to overlap the border of the main content
area. This wasn't happening, because the main area was rendered after the
logo and thus had a higher implicit z-index.
Final fix for overflowing PRE and IMG in articles

Finally, aligning the main container to the right fixes all problems with
overflows. PRE will now correctly show a scrollbar when content is wider,
IMG will just overflow and require some scrolling on narrow screens. Text
is rendered within the screen view, correctly.