resumeIn brief
grid-auto-columns sets a size or repeating pattern for columns created outside the explicit grid definition. This matters during automatic placement or placement at a more distant column.
Useful to know
grid-auto-columns sets a size or repeating pattern for columns created outside the explicit grid definition. This matters during automatic placement or placement at a more distant column. [1]
If a new column differs from others, check whether it is implicit. Editing only grid-template-columns does not necessarily size every additional column as intended.
Sources
For further detail and to check the information: