Hide Side Bar (Undo) and add any Full Background image - Twine game engine

Take Codes for your game from here. 

Hide Side Bar (Undo button) code : tw-sidebar {visibility: hidden}

Add any Background images : tw-story {background-image:url("Add your own Copy Image Address here");

 background-size:cover;}

<Credit to original Code creator> 

You will need to add those Codes in Stylesheet of Twine game engine. 

Tutorial is also provided in details.