I don’t use Dreamweaver, I know they updated it to be more like an actual editor but I would still not use it. I’d suggest using VS Code and using the Live Server extension.
Anyway, are you sure the message isn’t expected rbrace in this column, if so, it may come from a lack of support for CSS grid by the code linter used to check for syntax errors.
As for the layout, it won’t fill the full with because of auto-fill you can use auto-fit instead.
grid-template-columns: repeat(auto-fit, minmax(38ch, 1fr));