I'm not sure if the only options are:

Enlarge the window.
Use this or an equivalent extension.

Windows 10 (x64) | Anniversary Update
Opera Stable · Beta · Developer
Test profile | Back up Linux · Mac · Win

Hey thanks for replying. I already use stylish extension for many sites, I have tried other minimalistic scrollbars before but it didn't work. The link you provided worked! Many thanks, you have gotten rid of my annoyance of the scrollbar.

I have been putting up with it for quite sometime, but I would like to get rid of the scrollbars that appear when using messenger sidebar. Here is a screenshot: http://prntscr.com/fldlk9
I know that zooming out would fix this problem, though I am not sure how to do that in the sidebar.

Any help would be greatly appreciated.

I am new to Opera, and am very confused as to how some things work. I would like to change the skin, but where do i change it? The manual says that it is under, "Tools>Appearance>Skins" but i don't understand where "tools" menu is. Also Because i Do not know where that menu is, I cannot enable: "Multiple Document Interface (MDI). This allows you to resize pages and tile them next to each other on the same workspace to compare or work with several pages. For instance, you can have a chat page open next to a page for browsing or composing an e-mail message. To use this feature, select Tools > Preferences > Advanced > Browsing and check “Show window menu”. The window menu allows you to manage the pages in the MDI." An answer to this will be greatly appreciated.