Opera is built on Chromium project. Chromium is an open  source project that uses WebKit, a free and open source rendering engine. WebKit is open sourced by Apple.

So, Google Chrome and Opera resemble a lot. They use process for each tab and look similar. The benefit of using processes to handle tabs is:

1. Better security for browser as processes can’t circumvent security rules easily.
2. Identification of inactivated tabs and swapping them out of memory, to keep browser light-weight.

To understand more about rendering and Chromium architecture, please visit the following:

1. https://www.chromium.org/developers/design-documents/multi-process-architecture
2. https://www.chromium.org/developers/design-documents/displaying-a-web-page-in-chrome