packages/jss/src/utils/toCss.js
function indentStr(str: string, indent: number): string {
  let result = ''
  for (let index = 0; index < indent; index++) result += '  '
  return result + str
}
function indentStr(str: string, indent: number): string {
  let result = ''
  for (let index = 0; index < indent; index++) result += '  '
  return result + str
}
Indent a string.
http://jsperf.com/array-join-vs-for