code: function findRems(rule) {
  
          for (var i = 0; i < rule.declarations.length; i++) {
            var declaration = rule.declarations[i];
  
            // grab values that contain 'rem'
            if (declaration.type === 'declaration' && isSupported(declaration) && regexRem.test(declaration.value)) {
  
              var pxValues = remToPx(declaration.value.split(/\s(?![^\(\)]*\))/));
  
              if (options.replace) {
                declaration.value = pxValues;
              } else {
                var fallback = clone(declaration);
                fallback.value = pxValues;
                rule.declarations.splice(i, 0, fallback);
              }
  
            }
          }
        }
docs: look for rem values