Have one column in content width, let the other(s) take the remaining space

.grid {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr) auto;
}

Not using minmax(0, 1fr) but just going with 1fr allowes the content to break out of the container (grey background). This is, because 1fr is shorthand for minmax(auto, 1fr).

With 1fr only (i.e. minmax(auto, 1fr)):

With minmax(0,1fr) (which isn't great either but illustrates the point):

Reference:

• This StackOverflow thread asking the exact question