[Theme – Ink] Having trouble with setting a custom background!

Hi, I’m currently using the Ink theme and I’m really struggling with implementing a custom background for the home page, kinda a newbie here but you gotta start sometime haha.

I’ve set a JPG file linked by custom CSS in the Stylesheet, and the background image appears behind the theme’s default background (white), I know this because there is a responsive menu, and when I click the menu button, the page slides to the left and my menu appears, and for a second or two I can see my custom background image behind everything else!

How do I only have my custom background image appear and not the theme’s default? and how do I make it appear in front of everything not behind?

Thanks.