What is the CSS property that makes a fully enclose it's contents?

What is the CSS property that makes a fully enclose it's contents?

I am using <fieldsets> to group but it always gives me a message in the
IDE saying that the <legend> is missing. I decided to try and simulate the
<fieldset> with a <div>.
.grid-select .group {
border: 1px solid #d9d9d9;
padding: 12px;
-webkit-background-clip: padding-box;
-moz-background-clip: padding-box;
background-clip: padding-box;
-webkit-border-radius: 0.25em;
-moz-border-radius: 0.25em;
border-radius: 0.25em;
margin-bottom: 1.667em;
position: relative;
z-index: 89;
padding-top: 1.667em;
}
This does not work for me as it seems like the does not wrap around the
inside my fieldset at all.
Is there some other property that a <fieldset> has that I don't have?