CSS-0.5px 边框

<div class="border">hello world</div>

 .border {
            width: 150px;
            height: 40px;
            border-radius: 4px;
            text-align: center;
            line-height: 40px;
            color: deepskyblue;
            position: relative;
        }

        .border::after {
            content: '';
            display: block;
            width: 200%;
            height: 200%;
            border: 1px solid deepskyblue;
            transform: scale(0.5);
            position: absolute;
            left: 0;
            top: 0;
            transform-origin: 0 0;
        }

效果：