<div class='thin-border'></div>
.thin-border {
position: relative;
width: 40px;
height: 20px;
}
.thin-border::after {
content: ' ';
position: absolute;
left: 0;
top: 0;
border: '1px solid #000';
border-radius: 4px;
box-sizing: border-box;
width: 200%;
height: 200%;
transform: scale(.5);
transform-origin: left top;
}
在使用前可以先增加 window.devicePixelRatio && window.devicePixelRatio >= 2 的判断，建议像素比在 2 及已上时使用