Style updates

[aazuspan]

Closes #43

• Slight style tweaks with font opacity and implementing the hover background color from the Code Editor
• Explicitly set font-size and margins to avoid inheriting incompatible styles
• Use a longer class name for the top-level div to avoid clashes. The internal class names (ee-k and ee-v) are still short to reduce repr size (they add up when you have thousands of objects), but those are more unique already so I'm not too worried.