Shop Buklder: section custom CSS add characters in the value field

[fcpxstudio]

Working with the website builder, I try to add a custom css on a media section (my store is builed on the Impact theme but I think the error is on shopify side). I want to change the grid-template-columns proprety of a media section, here is my custom css code:

media-grid {
  grid-template-columns: minmax(160px, auto) auto auto;
}

Once saved, the change doesn't work and a strange tag is added in the css code when I inspect the page with Chrome DevTool:

The tag #shopify-section-template--18056017772842__media-grid  has been added in the minmax value. That create an error and disable the line.

Everything works fine if I manually remove the tag with the DevTool. Does someone knows why this tag is being added and how to fix this issue? Any hint is welcome.

Thank you.

UPDATE: The same tag is added in each minmax value I write in this custom CSS section.