css3实现圆角边框渐变

<button class="border">112233</button>

.border{
	position: relative;
	border: 4px solid transparent;
	border-radius: 16px;
	background: linear-gradient(orange, violet);
	background-clip: padding-box;
	padding: 10px;
	/* just to show box-shadow still works fine */
	box-shadow: 0 3px 9px black, inset 0 0 9px white;
}
.border::after{
	position: absolute;
	top: -4px; bottom: -4px;
	left: -4px; right: -4px;
	background: linear-gradient(red, blue);
	content: '';
	z-index: -1;
	border-radius: 16px;
}