JSFiddle - React, Tailwind, and code Playground

HTML

<div id="halat-calc">
  <div class="form">
    <div>
      Тестовый блок
    </div>
  </div>
</div>

CSS

#halat-calc .form > div {
  background: red;
  width: 50%;
}

@media(max-width: 426px){
  #halat-calc .form > div {
    width: 100% !important;
    display: block !important;
    float: none !important;
    background: green;
  }
}