JSFiddle - React, Tailwind, and code Playground

HTML

<div id="graph_container">
  <div id="car_select"> 
  # this part is at the correct location...     
  </div>

  <div id = "graph">
  # this is now inside the container too 
  </div>
    
    <div class="clear"></div>
</div>

CSS

#graph_container{
  width: 75%;   
  margin: 0 auto;
  background-color: #FFF;
  padding: 20px 40px;
  border: solid 1px black;
  margin-top: 20px; 
}

#graph{
  float: right;
  width: 75%;
  margin-top: 20px;
  background-color: blue;
}

#car_select{
  float: left;
  width: 25%;   
  margin: 0;
  background-color: red;
}

.clear {
  clear: both;   
}