Here are some Opencart demos we like (:
This PDF Wizard basic (ocmod extension) adds the ability to download invoices in PDF format on both of your admin/frontend Opencart websites. Colors and font families can be altered to match your stores design.
Opencart 3 (currently) ships with Bootstrap 3. This is mostly a tech preview of Bootstrap 4 with the hopes of adaption into future Opencart releases. We love Opencart and Bootstrap and want to keep both of these beautiful pieces of software moving into the future!