JSFiddle - React, Tailwind, and code Playground

HTML

<div class=container>
  <div id=left>No matter how big the left or right text gets</div>
  <div id=center>KEEP ME IN THE DEAD CENTER</div>
  <div id=right>foobar</div>
</div>

CSS

.container {
  padding: 0;
  margin: 0;
  display: flex;
  flex-direction: row;
  justify-content: center;
  align-items: center;
  position: fixed;
  bottom: 0;
  width: 100%;
  background-color: lightgray;
}

#left,
#right,
#center {
  display: flex;
  margin: 1px;
  padding: 5px;
  background-color: lightblue;
}

#left {
  background-color: salmon;
}
#center {
  background-color: lightgreen;
}