Install the Bootstrap theme. Get it from:
https://www.drupal.org/project/bootstrap
(Use the latest stable version for Drupal 8. At the time of writing that was 8.x-3.0-beta2.)
Set it as your default theme. Pick one of the variants on the Advanced settings tab. Cerulean, Cosmo…
If you’ve placed any blocks (custom, communications control, etc.) you will want to make sure they still appear correctly, since regions and block placing are theme specific.
Upload the URL of your site.
(If you were logged in as a student, you could submit an exercise solution, and get some feedback.)
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