How to override global CSS in a CSS module file?

Since .flex refers to a global class you’ll need to use the :global selector to target it in your CSS module.

/* Layout.module.css */

.navbar :global(.flex) {
    justify-content: space-between;
}

Or using an alternate syntax.

.navbar {
    :global {
        .flex {
            justify-content: space-between;
        }
    }
}