SOURCE

<div class="felx">
    <div class="black-left">
        <div class="left-top"></div>
    </div>
    <div class="black-mid">
        <div class="top"></div>
    </div>
    <div class="black-right"></div>
</div>

body{
    background: #fff
}
.felx{
    position: relative;
    display: flex;
    margin-top: 50px;
    align-items: flex-end;
}
.left-top{
    position: absolute;
    top: 0px;
    right: -22px;
    background: black;
    width: 60px;
    height: 60px;
    border-radius: 6px;
    transform: skew(40deg);
    z-index: 1;
}
.top{
    position: absolute;
    top: -30px;
    right: -5px;
    background: #fff;
    width: 60px;
    height: 60px;
    border-radius: 10px;
    transform: skew(40deg);
}
.black-left{
    position: relative;
    width: 300px;
    height: 200px;
    background: black;
    border-radius: 6px 10px 0 6px;
    z-index: 10;
}
.black-mid{
    position: relative;
    width: 50px;
    height: 200px;
    background: black;
    border-radius: 10px 6px 0 0
}
.black-right{
    width: 20px;
    height: 170px;
    background: black;
    border-radius: 0 6px 6px 0
}