.block-left {
  width: 100%;
  max-width: 768px;
  height: auto;
  float: left;
  position: relative;
}

 @media only screen and (min-width: 768px) {
  /* For desktop: */
  .block-left {
    width: 50%;
    height: auto;
    float: left;
    margin-right: 40px;
  }
  }