<style>
    div {
        width: 100px;
        height: 100px;
    }

    /* Both of these border-widths should snap to 1px. */
    .a {
        border: 1.8px solid black;
    }
    .b {
        border: 0.2px solid black;
    }
</style><div class="a"></div><div class="b"></div>