Set the image's dimensions in the css

This also sets the height to 'auto' rather than some hardcoded value.
That way, we can hope to get a nice layout even when we override the
width via css.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Add styles for small screens

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Run grunt again

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>