Make a grid item span to the last row / column in implicit grid

Is it possible to make a grid item span from the first to the last row when I don’t know the number of rows?

A natural Grid solution to this problem appears to be missing in the current spec (Level 1). So the answer would be “no”, strictly with Grid properties.

However, as pointed out in this answer, it may be possible with absolute positioning.

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While CSS Grid cannot make a grid area span all columns / rows in an implicit grid, it can do the job in an explicit grid.

Use negative integers.

Here are two interesting sections in the CSS Grid specification:

7.1. The Explicit Grid

Numeric indexes in the grid-placement properties count from the edges
of the explicit grid. Positive indexes count from the start side,
while negative indexes count from the end side.

and here…

8.3. Line-based Placement: the grid-row-start, grid-column-start, grid-row-end, and grid-column-end properties

If a negative integer is given, it instead counts in reverse, starting
from the end edge of the explicit grid.

In other words, when dealing with an explicit grid, which is a grid that you define using these properties:

• grid-template-rows
• grid-template-columns
• grid-template-areas

… you can make a grid area span all columns by setting this rule:

grid-column: 3 / -1;

That tells the grid area to span from the third column line to the last column line.

The reverse would be:

grid-column: 1 / -3;

Again, this method works only in explicit grids.