<!DOCTYPE html>
<html>
<head>
<link rel="author" title="Sammy Gill" href="mailto:sammy.gill@apple.com">
<link rel="help" href="https://drafts.csswg.org/css-box-4/#margin-trim-block">
<meta name="assert" content="block-start should be trimmed for float that touches the top of the containing block">
<style>
container {
    display: block;
    width: 100px;
    height: 100px;
    border: 1px solid black;
}
item {
    width: 50px;
    height: 50px;
    background-color: green;
    float: left;
}
</style>
</head