媒体

html,
body,
svg {
  height: 100%;
}

<svg viewBox="0 0 240 220" xmlns="http://www.w3.org/2000/svg">
  <style>
    rect {
      fill: black;
    }
  </style>
  <style media="(width >= 600px)">
    rect {
      fill: seagreen;
    }
  </style>

  <text y="15">Resize the window to see the effect</text>
  <rect y="20" width="200" height="200" />
</svg>