grid-auto-columns

A property that specifies the default column size(s) for a container.

.grid-container {
  display: grid;
  grid-auto-columns: <col-value>;
}

where <col-value> can be one of the following:

• Grid keyword: auto, maxcontent, minmax()
• Pixel value: 300px
• Percent value: 25%
• Fractional unit value: 1fr

A container divided into evenly spaced columns with a minimum width of 100 pixels:

.content-a-container {
  display: grid;
  grid-auto-columns: minmax(100px, auto);
}

A container with columns that each constitute 10% of the available width:

.content-b-container {
  display: grid;
  grid-auto-columns: 10%;
}