JSFiddle - React, Tailwind, and code Playground

HTML

<div id="wrapper">
    <div class="content">
        <div id="work">
        
          <div class="piece-slide">
              <a class="piece">
                  <img src="https://athlonecommunityradio.ie/wp-content/uploads/2017/04/placeholder.png">
              </a>
          </div>
          
          <div class="piece-slide">
              <a class="piece">
                  <img src="https://dummyimage.com/hd1080https://dummyimage.com/hd1080">
              </a>
              <a class="piece">
                  <img src="https://dummyimage.com/hd1080https://dummyimage.com/hd1080">
              </a>
          </div>
          
          <!-- THIRD DIV WHERE WIDTH SHOULD BE SET  -->
          <div id="third-div" class="piece-slide">
              <a class="piece" num="1">
                  Nested Element 1<img src="http://i.stack.imgur.com/yZlqh.png">
              </a>
              <a class="piece" num="2">
                  Nested Element 2<img src="http://www.jennybeaumont.com/wp-content/uploads/2015/03/placeholder.gif">
              </a>
              <a class="piece" num="3">
                  Nested Element 3<img src="http://suplugins.com/podium/images/placeholder-02.jpg">
              </a>
          </div>
          <div class="piece-slide">
              <a class="piece">
                  <img src="https://athlonecommunityradio.ie/wp-content/uploads/2017/04/placeholder.png">
              </a>
          </div>
        </div>
      </div>
</div>

CSS

#wrapper {
    display: flex;
    flex-direction: column;
    height: 100vh;
}
.content {
    flex: 1;
}
#work {
    height: 100%;
    overflow-x: scroll;
    display: flex;
    background-color: red;
}

.piece-slide {
    display: flex;
    align-items: center;
    position: relative;
    padding-right: 5em;
    box-sizing: border-box;
    border-right: 1px solid black;
}

.piece {
    width: 25vw;
    margin: 10px;
}

.piece img {
    max-width: 100%;
}

#third-div {
    /* D0ES NOT WORK */
    width: 100vw;
    background-color: green;
}

#third-div a {
    position: absolute;  
}
#third-div a:nth-child(1) {
    top: 0;
    left: 0; 
}
#third-div a:nth-child(2) {
    top: 25vw;
    left: 25vw; 
}
#third-div a:nth-child(3) {
    left: 60vw; 
}

JavaScript

$( "#third-div").outerWidth("100vw");