.grid-row {
  /* contain floats */
  overflow: hidden;

  /* compensate column padding & margin */
  margin-top: -1em;
  margin-right: -0.5em;
  margin-left: -0.5em;
}

img {
    max-width: 100%;
    max-height: 100%;
}

.grid-col {
  float: left;
  width: 100%;

  /* don't add padding to width */
  box-sizing: border-box;

  /* column gutter */
  padding: 0 0.5em;
  margin-top: 1em;
}

.one-half {
  width: 50%;
}

.one-third {
  width: 33.33333%;
}

.two-thirds {
  width: 66.66667%;
}

.one-fourth {
  width: 25%;
}

.three-fourths {
  width: 75%;
}