<svg width="500" height="200" viewBox="0 0 150 40" xmlns="http://www.w3.org/2000/svg">
  <style>
    text  { font: italic 12px serif; }
    tspan { font: bold 10px sans-serif; fill: red; }
  </style>

  <text x="0" y="30" class="small">
    You are
    <tspan>not</tspan>
    a banana!
  </text>
</svg>