The HTML fieldset tag is not working in display flex, order property. But it works with a div tag. 
.fset {
  display: flex;
}
.fset .first {
  order: 2;
  -webkit-order: 2;
}
.fset .second {
  order: 1;
  -webkit-order: 1;
}<fieldset class="fset">
  <div class="first">
    <p>first</p>
  </div>
  <div class="second">
    <p>second</p>
  </div>
</fieldset> 
    