<style>
        section{
            width: 160px;
            height: 140px;
            border: 1px solid rgba(179, 179, 179, 0.404);
            box-shadow: 5px 5px 20px rgba(179, 179, 179, 0.404);
            margin: 50px auto;
        }
        div.bg{
            width: 150px;
            height: 100px;
            background-color: red;
            margin: 20px auto;
            position: relative;
        }
        div.bg div.tri{
            width: 0;
            height: 0;
            border: 14px solid transparent;
            border-top: 10px solid yellow;
            transform: translateX(20px) translateY(20px);
        }
        div.bg div.tri::before{
            content: '';
            position: absolute;
            width: 0;
            height: 0;
            border: 14px solid transparent;
            border-left: 10px solid yellow;
            transform: rotate(21deg) translateX(-11px) translateY(-14px);
        }
        div.bg div.tri::after{
            content: '';
            position: absolute;
            width: 0;
            height: 0;
            border: 14px solid transparent;
            border-right: 10px solid yellow;
            transform: rotate(-21deg) translateX(-11px) translateY(-22px);
        }
        div.bg div.tri:nth-child(1){
            transform: translateX(13px) translateY(33px);
        }
        div.bg div.tri:nth-child(2){
            transform: rotate(20deg) translateX(25px) translateY(-28px) scale(.4);
        }
        div.bg div.tri:nth-child(3){
            transform: rotate(40deg) translateX(16px) translateY(-51px) scale(.4);
        }
        div.bg div.tri:nth-child(4){
            transform: rotate(71deg) translateX(-18px) translateY(-54px) scale(.4);
        }
        div.bg div.tri:nth-child(5){
            transform: rotate(20deg) translateX(19px) translateY(-51px) scale(.4);
        }
    </style>

​<section>
        <div class="bg">
            <div class="tri"></div>
            <div class="tri"></div>
            <div class="tri"></div>
            <div class="tri"></div>
            <div class="tri"></div>
        </div>
</section>