hi guys, i managed to change them via windows personalization -> windows color & appearance -> advance appearance setting it's under "Menu" which determines the gap between each row, however the size is limited by the font size & type.
however everything now looks different. the rest of the menu fonts also shrunk when i reduce the size & font for "Menu".
so i'm guessing whatever made the change was done on Opera 12.18, it did not change the font size however it changed the "gap" between each menu content (File/Edit/View/Bookmark etc dropdown) & right click context menu resulting each row of dropdown taking more space so what used to be 2 page bookmark is now 3 pages.
i've spent few hours trying to figure it out and i'm abit tired.
what i did was i installed this Touchmote program that is designed for some controllers like wiimote to be used on PC as a touchpad, it activated this flick on windows (which i disabled) but seeing only Opera is affected i'm not sure how to solve the issue.