Edit in JSFiddle

<h2>background-clip: border-box;</h2>
<div id="border-box">
    <p>This paragraph is the content.</p>
</div>

<h2>background-clip: padding-box;</h2>
<div id="padding-box">
    <p>This paragraph is the content.</p>
</div>

<h2>background-clip: content-box;</h2>
<h3>browser default paragraph margins</h3>
<div id="content-box">
    <p>This paragraph is the content.</p>
</div>

<h2>background-clip: content-box;</h2>
<h3>外边距设置为0</h3>
<div id="content-box">
    <p class="nomargin">This paragraph is the content.</p>
</div>

div {
    background-color: yellow;
    width: 225px;
    padding: 1em 0;
    border: 5px solid rgba(156, 224, 251, .5);
}

.nomargin {
    margin: 0;
}

#border-box {
    background-clip: border-box;
}

#padding-box {
    background-clip: padding-box;
}

#content-box {
    background-clip: content-box;
}


/* styling for the Pen, unrelated to background-clip */

body {
    font-family: sans-serif;
}

div {
    margin-bottom: 2em;
}