div{
    border: 3px solid #3CC;
    margin: 10px 10px;
    height: 100px;
    background-color: #fff;
    color: #fff;
}

.fl{
    display: flex;
    justify-content: center;
    align-items: center;
}
.gd{
    display: grid;
    justify-content: center;
    align-items: center;
}

p{
    margin: 0px
}
.rel{
    position: relative;
}
.rel p{
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}