I think you didn't write it completely wrong
But it's better to use body instead of html.
Explanation why to use body
It allows you to use an overlay on top of that body tag. Like a grid-ish background on the body and a shade on the side. But both are correct. Depending on what you are trying to do ofc.
If you don't repeat your background there is a possibility that your picture doesn't use the whole page and then you should use the html tag. But in this case it gives the same solution because of that repeat.
SO replay: tnx to attronics
Explanation of your 'error'
If your images are in a different folder than your html page (which should be the case).
You should use ..
as relative path to your css file.
Without the ..
it would mean that you are going to look for that image in the same folder as your html page.
body{
background-image:url(../images/background-grid.jpg);
background-repeat:repeat;
}
Here is a site that gives some Basics of CSS. Didn't check the source though.