how to use "background-size : contain" in shorthand property with background with url.?

Question

below css is working with contain as it 's separately given as background-size but not by using the shorthand given in background

even i also eager to know the the parameters' sequence for background property in CSS

body { 
    background: #00ff00 url("smiley.gif") no-repeat fixed center;
    background-size:contain,contain; 
}

 body { 
    background: #00ff00 url("smiley.gif") no-repeat contain,contain fixed center; 
}  

but this is not working as i tried this shorthand method as above 

<p>This is some text</p>
<p>This is some text</p>
<p>This is some text</p>
<p>This is some text</p>
<p>This is some text</p>
<p>This is some text</p>
<p>This is some text</p>
<p>This is some text</p>
<p>This is some text</p>
<p>This is some text</p>
<p>This is some text</p>
<p>This is some text</p>
<p>This is some text</p>
<p>This is some text</p>
<p>This is some text</p>
<p>This is some text</p>
<p>This is some text</p>
<p>This is some text</p>
<p>This is some text</p>
<p>This is some text</p>
<p>This is some text</p>
<p>This is some text</p>
<p>This is some text</p>
<p>This is some text</p>

there is not an issue to use separately but need to know that whether any way to use background-size:contain in shorthand background property

even you can just check it out by making change in W3School's example here is the url for it

click to check your way

Answer 1

background: #00ff00 url("smiley.gif") no-repeat fixed center / contain; 

this should work.