SOURCE

<div class="box">
    <span class="item"></span>
    <span class="item"></span>
    <span class="item"></span>
</div>

.box {
    width: 100px;
    height: 100px;
    background-color: white;
    border-radius: 5px;
    margin: auto;
    position: relative;
}
.box>span:nth-child(1) {
    width: 20px;
    height: 20px;
    border-radius: 10px;
    position: absolute;
    top: 1vh;
    left: 1vw;
    background-color: black
}
.box>span:nth-child(2) {
    width: 20px;
    height: 20px;
    border-radius: 10px;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    background-color: black
}
.box>span:nth-child(3) {
    width: 20px;
    height: 20px;
    border-radius: 10px;
    position: absolute;
    bottom: 1vh;
    right: 1vw;
    background-color: black
}