JSFiddle - React, Tailwind, and code Playground

HTML

<div class="background-size">



  <div class="outside">

    <div class="inside">
      <p>
        This div must go full "background-size" width. Help!
      </p>
    </div>

  </div>
</div>

CSS

.background-size {
  background-color: #424243;
  width: 100%;
  height: 50vh;
}

.outside {
  background-color: #4286f4;
  height: 10vh;
  max-width: 500px;
  margin: auto;
}

.inside {
  background-color: #ababab;
  width: 100vw;
  transform: translateX(-50%);
  margin-left: 50%;
  height: 100%;
  z-index:1;
}