Design suggestion

[frannyfra]

The background image was stretching when resizing the screen.
You could fix it setting the background-size to cover;

Once you do it you will see that your image will not cover anymore the entire body, try to set a body height for that.

Last step, to prevent your container to move-slide across the background when resizing , try to use

background-position: center

background-position: center;
background-size: cover;
height: 100vh;