Opera 19 developer stream has been released and available for download for Mac and Windows. This version has added "Advanced Settings" option to "Settings" which allows user to control "use hardware acceleration option when available" under "System" and "disable tab bar’s top spacing when browser window is maximized" under User Interface. Opera team promises to introduce more options for power-users in future.
Read: How to install Themes in Opera 18+
You can download Opera developer from here.