How to get a column to span until the last grid line in an auto-flow grid? With an explicit grid, one can reference the -1 line, but it doesn’t seem to work with auto-flow. Here’s the code:

<div class="container">
  <div class="side"></div>
  <div>Row 1</div>
  <div>Row 2</div>
  <div>Row 3</div>
  <div>Row 4</div>
  <div>Row 5</div>
</div>

.container {
    display: grid;
    /* auto-flow doesn't work. */
    grid: auto-flow / 200px 50px;
    /*
        Explicit grid works.
        grid: repeat(5, auto) / 200px 50px;
    */
}

.side {
    /* Works in auto-flow if -1 is replaced with 6. */
    grid-area: 1 / 2 / -1;
    background-color: lightgrey;
}

If the grid is specified explicitly, everything works:

In an auto-flow grid, the column spans just a single row. (DevTools show that negative line numbers are assigned only to columns but not to rows, cf. the explicit grid image above.)