Full background images

First of all – what kind of layout do you have choosen on Enfold: General Layout : a stretched or a boxed or at the end a fixed frame layout?
If you have a boxed layout f.e. – you will have then on General Styling a “Body Background” Option

But this is only one part of your example page.
If you like to have a full transparent content – like on your example page there had to be a lot of css settings to be made.

best would be if you start with that boxed layout – it is possible to have this with a fixed frame.
It is hard to have this with a slideshow in the background..
That was my old attempt to reach this – but the slideshow timing will not be synchronized the more time passes:
https://webers-testseite.de/goldfinger/
( These are two identical slideshows that runs on theory synchronized – the one on top shows only a narrow strip and has a high z-index – the other has a low z-index)
But that is not necessary for your solution with a static background-image.
It will be best to help you if we can see the page it concerns.
it is easy to have a body background-image via quick css f.e. and even to have more than one background-image on the same container:
you see on that page how it is done for a 1/1 container with three background-images and different settings :
https://webers-testseite.de/multiple-background-images/

in other words it is possible to have this http://naturkosmetik-studio.at/Images/IMG_background.png as one background pattern that is set to repeat or not to scroll away – and those leaves too but with no repeat.

for background-attachment : fixed
there is a better way to have it – because on IOS Devices – this looks strange – on scrolling it flickers
( google on that background-attachment : fixed and Safari Browsers )

there is a little trick to have that: the background-image that should have background-attachment : fixed goes to the pseudo container :before –
and that container is set to position fixed!
So the code above will look like this ( for my page-id ) :

#top.page-id-38479 {
  background-image: url(https://webers-testseite.de/wp-content/uploads/IMG_bg.jpg);
  background-repeat: repeat;
  background-position: center center;
  background-attachment: scroll;
}

#top:before {
  background-image: url(https://webers-testseite.de/wp-content/uploads/IMG_background_treatments.png);
  background-repeat: repeat-y;
  background-position: left top;
  content: "";
  position: fixed;
  width: 100%;
  height: 100%;
  -webkit-clip-path: inset(0 0 0 0);
          clip-path: inset(0 0 0 0);
}

#top.page-id-38479 #main {
  background-color: rgba(255,255,255,0.2) !important;
}

#top.page-id-38479 .main_color {
  background-color: transparent !important;
}

.html_stretched #top.page-id-38479  #wrap_all {
  background-color: transparent !important;
}

with the fixed image on repeat-y now