<section>
  <!-- Header should wrap to second if needed, based on how much button element uses space -->
  <h1>
    Dynamic text that should wrap to second line if needed, because the text is sometimes pretty long
  </h1>
  <!-- Button should use as much space as possible to fit the text on one line-->
  <button>
    Dynamic button text
  </button>
</section>


section {
  width: 600px;
}

h1 {
  float: left;
  /* Width can't be used here, cos the texts are different length at different times */
  width: 400px;
}

button {
  float: right;
  margin-top: 20px;
}