v6.css

/* Non relevant styles - comments werent like this in codepen // */
* {
  box-sizing: border-box;
}

body {
	background-image: url("pattern_background.png");
	background-repeat: repeat; /* -y repeat-x;*/
}

p {
  font-size: 20px;
  font-family: sans-serif;
  color: white;
}

.container {
  padding: 100px 30px;
  width: 100%;
  margin: 0 auto;
  max-width: 900px;
}


.header{
	display:grid;
	grid-template-columns: 50% 50%;
}

.intro{
	display:grid;
	grid-template-columns: 40% 60%;
}


/* Relevant styles*/
.image-stack {
  display: grid;
  position: relative; /* imperative for the overlapping to work*/
  grid-template-columns: repeat(12, 1fr);  /*12 columns - 1 fractional unit each*/ 
}

.image-stack__item--bottom {
  grid-column: span 12 / -1;/*4 / -1;*/  /*starts at span4 and continues to the end (-1 enables that)*/
  grid-row: 1;
  z-index: 0;
}


.image-stack__item--top {
  grid-row: 1;     /*the images are on teh same row*/
  grid-column: 1 / span 12; /*1 / span 8;*/ /*starts at beginning goes up to col. 8*/  
  padding-top: 81%;  /*slightly arbitrary keeps proportion once resized*/
  z-index: -1;
}

.image-stack__item--top-2 {
  grid-row: 1;     /*the images are on teh same row*/
  grid-column: 1 / span 12; /*1 / span 8;*/ /*starts at beginning goes up to col. 8*/  
  padding-top: 81%;  /*slightly arbitrary keeps proportion once resized*/
  z-index: 1; /* tells the browser to make this image on top*/
}

img {
  display: block;
  width: 100%;
  
}