html, body {

    width: 100%;

    height: 100%;

    display: flex;

}

​

div {

    width: 100px;

    height: 100px;

    margin: auto;

}

​

.normal {

    border: 1px solid #000;

    background: deeppink;

}

​

.demo {

    border: 1px solid #000;

    background: deeppink;

    clip-path: polygon(0 0, 100% 0, 0 100%, 0 0);

}

​

.triangle {

    background: deeppink;

    clip-path: polygon(0 0, 100% 0, 0 100%, 0 0);

}