Gallery caption overlay Customisation

Site URL: https://giraffe-tuna-mkef.squarespace.com/config/pages/website-tools/custom-css

Heya _ I am looking to change the layout of text overlay on my gallery to that have main tiles, subtext 1 and subtext . 

Can anyone help me customise the code below to achieve this. Many thanks Rachel

.gallery-grid-item {
  position: relative;
}
.gallery-caption.gallery-caption-grid-simple {
  position: absolute;
  top: 50%;
  transform: translateY(-50%);
  text-align: center;
  opacity: 0;
  transition: opacity 0.5s ease;
  color: #fff;
  pointer-events:none; 
}
.gallery-grid-item:hover .gallery-caption-grid-simple{
  opacity: 1;
}

.gallery-grid-item .gallery-grid-item-wrapper:after {
  content: '';
  width: 100%;
  height: 100%;
  background: rgba(0,0,0,0.5);
  display: block;
  position: absolute;
  top:0;
  opacity: 0;
  transition: opacity 0.5s ease;
  pointer-events: none;

}

.gallery-grid-item:hover .gallery-grid-item-wrapper:after {
  opacity: 1;  
}

.gallery-caption.gallery-caption-grid-simple h3 {
  color: white;
}

Use caption with this code