Fix css to make the pop-up window full screen

[KarishmaBothara]

Screen.Recording.2021-07-26.at.12.04.03.PM.mov

On Firefox while testing observed that, as we reduced the window size of pop-up, the very first time the screen is not visible unless we hover till the top, since polkadot extension pop-up window is full size, the hover happens immediately. We need to fix the window size or add some css magic to make it appear... Attaching the video of the same...