how to align content at center screen code example

Example 1: how to center an image element inside a block in css

img { display:block;
      margin-left: auto;
      margin-right:auto;
      }

Example 2: css image center

.container {
    position: relative;
    float: right;
    width: 100%;
    height: 250px;
    overflow: hidden;
}

.container img {
    position: absolute;
    top: 50%;
    left: 50%;
    width: auto;
    min-width: 100%;
    height: 100%;
    /* height: auto; */
    /* min-height: 100%; */
    margin-right: -50%;
    transform: translate(-50%, -50%);
    object-fit: contain;
    -o-object-fit: contain;
}