Fix typo: Perhapas --> Perhaps
adjust whitespace in MathBox.glsl.html
Fix example files to allow them to validate

The exception is Landscape.html, which remains invalid
for having a script tag after the closing html tag.
DRY: move examples' css to a separate file

The css was virtually identical for all example files.
Some of them also had a transition rule,
and two had a label class definition.
These extra styles were also added to the base style,
using classes to allow them to apply only when appropriate.