.post__content figure > img {
    display: block;
    margin: 0 auto;
}

.post__content figure {
  margin-left:auto;
  margin-right:auto;
}

.post__content figure.w50   { width:50%; }
.post__content figure.w50 > img { width:100%; height:auto; }

.post__content figure.w75   { width:75%; }
.post__content figure.w75 > img { width:100%; height:auto; }