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Monobook makes frequent use of line-height specifications using the unit "em".
While these lengths _are_ font-size-relative, which is good, the computed value,
and not the relative value is inherited by child elements, which is bad.

The problem becomes apparent when a child node uses a different font-size. E.g.
many boxes on Wikipedia use font-size:80%. However, because the computed value
of line-height is inherited, the line-height stays unchanged (i.e. too large).

The solution is to use plain number line-heights, i.e. "1.5" instead of "1.5em".
That way, the line-height will properly scale when the font-size is changed.

Here's the relevant section from the CSS2 spec:
http://www.w3.org/TR/REC-CSS2/visudet.html#propdef-line-height

  Values for this property have the following meanings:
  [...]
  <length>
      The box height is set to this length. Negative values are illegal. 
  <number>
      The computed value of the property is this number multiplied by the
element's font
      size. Negative values are illegal. However, the number, not the computed
value, is
      inherited.