Opera 55 on developer version has got an update, the settings page has got material design. Like the Chrome material design Settings page, the new settings page in Opera browser consists of two categories: Basic and Advanced.
Opera with material design Settings
Basic Settings offer the settings for block ads, wallpapers, Appearance, sidebar, Synchronization, search engines, making opera the default browser and startup options.

Advanced Settings section, hidden by default, but expands when you click on Advanced label, offer Settings for Privacy and Security, Passwords and Forms, VPN, Battery Saver, My Flow, search pop-up, video pop-out, Opera Turbo, start Page, user interface, Downloads, System, shortcuts and Reset Settings.

‘Search Settings’ search bar on top of the page lets you find the setting you’re looking for.
READ: Opera 54: Update & Recovery Option in Menu
Disable Material design settings in Opera
If you don’t like the new material design settings page in Opera browser and want the old or classic settings page back, you can, here is how.
1. Visit opera://flags/#new-md-settings

2. Select Disabled and relaunch Opera to see the old Settings page.
Apart from the new settings page, Opera developer 55 based on Chromium 67, also improved instant search feature. Meanwhile, Opera flow allows to connect one desktop/laptop with one mobile only, but not both to mobile. We don’t know when Opera adds multi-device connection support to flow.
Opera’s Instant Search is like Quick Commands in Vivaldi
How to Set up Flow in Opera Desktop browser
How to disable My Flow in Opera browser?
You can download latest Opera developer 55.0.2962.0 from here.