Add styles

[boblail]

This addon would probably do well to include some styles — but as little branding as possible. If specific details (font-face, text-color, whitespace) need to be specified by this addon (i.e. can't just be set to inherit or something like that), then it'd be good to define those with SCSS variables.

These are the CSS classes defined by this addon:

• search-box
  • search-box-input
  • search-box-hints
    • search-box-hint (incomplete)
    • search-box-hint-value
• search-modifiers
  • search-modifier-section
  • search-modifier
    • search-modifier-value
    • search-modifier-label