CSS

absolute center css

.btn__play {
	position: absolute
    top: 50%
    left: 50%
    transform: translate(-50%, -50%)
}

center absolute element

.child {
    position: absolute;
    top: 50%;  /* position the top  edge of the element at the middle of the parent */
    left: 50%; /* position the left edge of the element at the middle of the parent */

    transform: translate(-50%, -50%); /* This is a shorthand of
                                         translateX(-50%) and translateY(-50%) */
}

center absolute suedo element

 left: 50%;
position:absolute;
top:50%;
transform:translate(-50%,-50%);