walker1232,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
.only__one {
background-color: #FF00FF;
}
.more__than {
background-color: #00FF7F;
}
.item {
padding: 5px; height: 100px; width: 100px; margin: 4px;
}
.container {
border: 1px dashed Gray;
display: table;
}
</style>
<script>
window.addEventListener("DOMContentLoaded", function() {
var container = document.querySelectorAll(".container");
[].forEach.call(container, function(el) {
var item = el.querySelectorAll(".item"),
cls = ["only__one", "more__than"][+(item.length > 1)];
[].forEach.call(item, function(el) {
el.classList.add(cls)
})
})
});
</script>
</head>
<body>
<div class="container">
<div class="item"></div>
</div>
<div class="container">
<div class="item"></div>
<div class="item"></div>
<div class="item"></div>
</div>
</body>
</html>