Opera's been updated and looks so nice in my opinion (hooray for dark theme), they're calling it Opera Reborn
HTTP://i.imgur.com/bmLNL2T.png
Sidebar is optional and can choose what appears on it - kinda like a bookmarks bar, but for shortcuts to things in the browser like extensions/history/etc - and they've added facebook messenger and whatsapp to it as well, and you can resize the width of them and "dock" them on the side at the cost of less browsing space, or just open/close when needed.. While I won't use it for messaging, I get the reasoning for it:
Original message details are unavailable.
Browsing and chatting simultaneously is cumbersome and inefficient now, as you need to switch between tabs when responding to a message. We believe this needs to change. That’s why we bring you Opera Reborn, the first browser to allow messengers to reside within your browser, without the need to install any extensions or apps.
https://blogs.opera.com/desktop/2017/05/opera-is-reborn/
There are some other changes mentioned in that link too, if you're interested, and some under the hood stuff here:
https://dev.opera.com/blog/opera-45/
Also the sidebar sits quite nicely in line with the windows button with small taskbar buttons turned on
HTTP://i.imgur.com/4IzTg46.png