Express is now at the end of life phase and it will be removed from sandbox sites on June 05, 2018, and removed from production sites on July 12, 2018. At those points, you would not be able to access or use the Express theme.
You should have received communications previously reminding you of your options for themes after July 2018. We recommend the following videos and documentation for each of the alternative themes if you want to explore more about them.
If you have any additional questions or would like to speak with a Moodlerooms representative, please contact us directly via a support ticket or though your support specialist.
With the Express theme, you are provided with branding capabilities for both basic and advanced users with tools to completely customize the appearance of the institution's site, course categories, and courses. With the Express theme, the Express block is added to your institution site, and you have more control of design of your website over any other Moodle/Moodlerooms theme.
An Express design is what is displayed as the look and feel for the institution site, category, or course when a user views a page. Express designs are created from Express templates, which are predefined page structures and layouts with a selection of color variants that, when selected within the Express blocks Create a Design tab, create an Express design for the site, category, or course. Express templates provide clients with the ability to approve specific page structures and layouts while allowing their teachers to feel empowered to create a unique look for their course by selecting different color variations to develop their own design.