Syntax Error: Error: expected

I'm trying to get this to work:

$container-max-widths: ( sm: 540px, md: 720px, lg: 960px, xl: 1140px, xxl: 1610px );

The error I got is

Syntax Error: Error: expected ")". ╷ 1 │ $container-max-widths: (; │ ^ ╵ stdin 1:25 root stylesheet

Any help appreciated.