<style>
	.demo_css_sprt:first-child	{
		margin-bottom: 1em;
	}
	.demo_css_sprt, .demo_css_sprt div	{
		border: dotted 1px red;
		padding:1em;
	}
	.demo_css_sprt div	{
		margin: 1em 0;
	}
	.demo_css_sprt p	{
		border: dashed 1px blue;
		padding:1em;
	}
	.demo_css_sprt p:only-child	{
		background: mistyrose;
	}
</style>
<div class="demo_css_sprt">
	要素1
	<div>要素2</div>
	<p>要素3</p>
</div>
<div class="demo_css_sprt">
	<p>要素4</p>
</div>