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#star-six {
    width: 0;
    height: 0;
    border-left: 50px solid transparent;
    border-right: 50px solid transparent;
    border-bottom: 100px solid red;
    position: relative;
}
#star-six:after {
    width: 0;
    height: 0;
    border-left: 50px solid transparent;
    border-right: 50px solid transparent;
    border-top: 100px solid red;
    position: absolute;
    content: "";
    top: 30px;
    left: -50px;
}