小编Yas*_*ari的帖子

.contact {
    flex-grow: 2;
    z-index: 2;
    position:relative;
    display: block;
    margin: 40px 40px;
    padding: 60px; 
    text-align: center;
    background-color: #343434;
}

.bevel {
    overflow:hidden;
    clip-path: polygon(
        0 10%,
        10% 0,
        90% 0,
        100% 10%,
        100% 90%,
        90% 100%,
        10% 100%,
        0% 90%,
        0% 10%);
}

<form id="contact" class="contact bevel">
  <!-- content makes up width and height --!>
</form>