minmax()

grid-template-columns: minmax(20px, auto) 1fr 1fr;

grid-template-columns: minmax(0, 1fr) minmax(0, 1fr) minmax(0, 1fr);

grid-template-columns: minmax(2ch, 10ch) 1fr 1fr;

<section class="default-example" id="default-example">
  <div class="example-container">
    <div class="transition-all" id="example-element">
      <div>One. This column has more text in it.</div>
      <div>Two</div>
      <div>Three</div>
      <div>Four</div>
      <div>Five</div>
    </div>
  </div>
</section>

#example-element {
  border: 1px solid #c5c5c5;
  display: grid;
  grid-gap: 10px;
  width: 250px;
}

#example-element > div {
  background-color: rgb(0 0 255 / 0.2);
  border: 3px solid blue;
  text-align: left;
}

/* <inflexible-breadth>, <track-breadth> values */
minmax(200px, 1fr)
minmax(400px, 50%)
minmax(30%, 300px)
minmax(100px, max-content)
minmax(min-content, 400px)
minmax(max-content, auto)
minmax(auto, 300px)
minmax(min-content, auto)

/* <fixed-breadth>, <track-breadth> values */
minmax(200px, 1fr)
minmax(30%, 300px)
minmax(400px, 50%)
minmax(50%, min-content)
minmax(300px, max-content)
minmax(200px, auto)

/* <inflexible-breadth>, <fixed-breadth> values */
minmax(400px, 50%)
minmax(30%, 300px)
minmax(min-content, 200px)
minmax(max-content, 200px)
minmax(auto, 300px)

#container {
  display: grid;
  grid-template-columns: minmax(min-content, 300px) minmax(200px, 1fr) 150px;
  grid-gap: 5px;
  box-sizing: border-box;
  height: 200px;
  width: 100%;
  background-color: #8cffa0;
  padding: 10px;
}

#container > div {
  background-color: #8ca0ff;
  padding: 5px;
}

<div id="container">
  <div>Item as wide as the content, but at most 300 pixels.</div>
  <div>Item with flexible width but a minimum of 200 pixels.</div>
  <div>Inflexible item of 150 pixels width.</div>
</div>