In brief
grid-template-columns defines the explicit grid's columns. For example, 1fr 2fr distributes flexible shares, but content's minimum requirements also participate in sizing.
Useful to know
grid-template-columns defines the explicit grid's columns. For example, 1fr 2fr distributes flexible shares, but content's minimum requirements also participate in sizing. [1]
With a long unbroken value, do not expect those numbers alone to prevent overflow. Check minimum sizes and text wrapping alongside the column definition.
Sources
For further detail and to check the information: