<!doctype html>
<meta charset="utf-8">
<title>Blue Box with Green Frame</title>
<style>
    #a {
        width: 300px;
        height: 200px;
        position: absolute;
        left: 100px;
        top: 100px;
        border-width: 50px;
        border-style: solid;
        border-image: linear-gradient(green, green);
        background-color: blue;
        background-clip: content-box;
        border-image-slice: 33%;
        padding-left: 100px;
        padding-top: 50px;
        padding-right: 10px;
        padding-bottom: 50px;
    }
</style>
<div id="a"></div>