Make CSS Grid auto-fill only 2 columns

Question

I am using CSS Grid and have made the following layout in the codepen found here: https://codepen.io/alexg2195/pen/xLEeMd

My issue is that when using repeat(auto-fill, minmax(400px, 1fr)); I end up with a layout that goes beyond just two columns.

Is there a way to force two columns but still have the same min auto fill resize behaviors?

body {
  margin: 40px;
}

.layout {
  display: grid;
  grid-gap: 10px;
  grid-template-columns: 1fr 100px;
  grid-template-areas: "main btn" "main .";
}

.btn {
  grid-area: btn;
  background-color: #444;
  color: #ddd;
  border-radius: 5px;
  padding: 20px;
  font-size: 150%;
}

.boxes {
  grid-area: main;
  display: grid;
  grid-gap: 10px;
  grid-template-columns: repeat(auto-fill, minmax(400px, 1fr));
}

.box {
  background-color: #444;
  color: #fff;
  border-radius: 5px;
  padding: 20px;
  font-size: 150%;
}

<div class="layout">
  <div class="boxes">
    <div class="box a">A</div>
    <div class="box b">B</div>
    <div class="box c">C</div>
    <div class="box d">D</div>
    <div class="box e">E</div>
    <div class="box f">F</div>
    <div class="box g">G</div>
    <div class="box h">H</div>
    <div class="box i">I</div>
    <div class="box j">J</div>
    <div class="box k">K</div>
    <div class="box l">L</div>
    <div class="box m">M</div>
  </div>
  <div class="btn">BTN</div>
</div>

Answer 1

Is there a way to force two columns but still have the same min auto fill resize behaviors?

Not with auto-fill / auto-fit.

These functions are built to fit the largest number of tracks without overflowing the container.

7.2.2.2. Repeat-to-fill: auto-fill and auto-fit repetitions

When auto-fill is given as the repetition number, if the grid container has a definite size or max size in the relevant axis, then the number of repetitions is the largest possible positive integer that does not cause the grid to overflow its grid container.

In order to "auto-fill" a maximum of two columns per row, you'll need to find another method.

Maybe flexbox?

revised demo

body {
  margin: 40px;
}

.layout {
  display: grid;
  grid-gap: 10px;
  grid-template-columns: 1fr 100px;
  grid-template-areas: "main btn" "main .";
}

.btn {
  grid-area: btn;
  background-color: #444;
  color: #ddd;
  border-radius: 5px;
  padding: 20px;
  font-size: 150%;
}

.boxes {
  grid-area: main;
  display: flex;
  flex-wrap: wrap;
}

.box {
  flex: 1 0 40%;
  margin: 5px;
  background-color: #444;
  color: #fff;
  border-radius: 5px;
  padding: 20px;
  font-size: 150%;
}

div.box.n {
  visibility: hidden;    /* https://stackoverflow.com/q/42176419/3597276 */
  height: 0;
}

<div class="layout">
  <div class="boxes">
    <div class="box a">A</div>
    <div class="box b">B</div>
    <div class="box c">C</div>
    <div class="box d">D</div>
    <div class="box e">E</div>
    <div class="box f">F</div>
    <div class="box g">G</div>
    <div class="box h">H</div>
    <div class="box i">I</div>
    <div class="box j">J</div>
    <div class="box k">K</div>
    <div class="box l">L</div>
    <div class="box m">M</div>
    <div class="box n">N</div>
  </div>
  <div class="btn">BTN</div>
</div>