mixin container
    -
        let classes = {
            'l-container':            true,
            'l-container--narrow':    attributes.narrow,
            'l-container--narrow-75': attributes.narrow50,
            'u-themed':               !!attributes.theme
        }
        if (!!attributes.theme) {
            classes['t-' + attributes.theme] = true
        }
        if (attributes.class) {
            classes[attributes.class] = true
        }

    div(class=classes)&attributes(attributes)
        block