@import url(//fonts.googleapis.com/css?family=Roboto+Mono:400,700,100,100italic,300,300italic,400italic,500,500italic,700italic)
=roboto-mono($fw: 400, $ls: 0, $fs: null, $tx-rendering: true)
  // $fw: フォントの太さ, $ls: 字間, $fs: フォントスタイル
  font-family: 'Roboto Mono', mono
  font-weight: $fw
  @if not $ls == 0
    letter-spacing: $ls
  @if (not $fs == null)
    font-style: italic
  @if $tx-rendering
    text-rendering: optimizelegibility