This is work for me. So try this may be it will be also helpful for you.(single and multiple node).
<script>
var selectedElement = null;
function singleline() {
document.execCommand('formatblock', false, 'p')
var selectedNodes = [];
var sel = rangy.getSelection();
for (var i = 0; i < sel.rangeCount; i++) {
selectedNodes = selectedNodes.concat(sel.getRangeAt(i).getNodes());
$(selectedNodes).css("height", "20px");
}
selectedElement = window.getSelection().focusNode.parentNode;
$(selectedElement).css("height", "20px");
}
</script>