code: function flattenRules(rules) {
    var out = {};
  
    rules.forEach(function(rule) {
      // Ignore anything that doesn't look like a CSS rule
      if (rule.type !== 'rule') return;
      rule.selectors.forEach(function(sel) {
        if (!out[sel]) out[sel] = {};
  
        rule.declarations.forEach(function(decl) {
          out[sel][decl.property] = decl.value;
        });
      });
    });
  
    return out;
  }
docs: ## flattenRules
  
  Flattens out all the rules in a CSS file so we can easily grab
  rules for a particular selector.
  
  @param {Array} rules Array of rules parsed by **css**
  @return {Object} Selctor -> property/value list