4. 边框内圆角

常规方法

用2个div

<div class="something-meaningful"><div>
I have a nice subtle inner rounding,
don't I look pretty?
</div></div>
.something-meaningful {
background: #655;
padding: .8em;
}
.something-meaningful > div {
background: tan;
border-radius: .8em;
padding: 1em;
}

outline + box-shadow

outline不会贴合圆角
box-shadow填补圆角

outline: .6em solid #655;
border-radius: .8em;
box-shadow: 0 0 0 .4em #655; /* todo calculate max of this */
background: tan;