You’ve got a lot of parentheses already in there, but believe it or not, you are still missing a pair. Remember, linear-gradient is a function and thus you need to use parentheses to pass arguments into it.
Also, CSS is very picking about spaces with functions. You can’t have a space between the function name and the opening parens.
If what I said above doesn’t quite ring a bell then open the last step of the CSS Color Markers course you already completed and you will see several examples of using the linear-gradient function.