Check out example codes for "css play button on image". It will help you in understanding the concepts better.

Code Example 1

.more_video_img {
  position: relative;
}

.playBtn {
  position: absolute;
  width: 40px;
  height: 40px;
  left: 50%;
  top: 50%;
  margin-left: -20px; /*half of the width */
  margin-top: -20px; /*half of the height */
}

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