Ghost/ghost/admin/app/components/gh-alert.js

import Component from '@ember/component';
import {computed} from '@ember/object';
import {inject as service} from '@ember/service';

export default Component.extend({
    notifications: service(),

    classNameBindings: ['typeClass'],
    classNames: ['gh-alert'],
    tagName: 'article',

    typeClass: computed('message.type', function () {
        let type = this.get('message.type');
        let classes = '';
        let typeMapping;

        typeMapping = {
            success: 'green',
            error: 'red',
            warn: 'blue',
            info: 'blue'
        };

        if (typeMapping[type] !== undefined) {
            classes += `gh-alert-${typeMapping[type]}`;
        }

        return classes;
    }),

    actions: {
        closeNotification() {
            this.notifications.closeNotification(this.message);
        }
    }
});