Page Template:Main page/shared/styles.css must have content model "Sanitized CSS" for TemplateStyles (current model is "wikitext").
<img src="image1.jpg" alt="Card Image 1">
Card Title 1
This is some description for Card 1.
<img src="image2.jpg" alt="Card Image 2">
Card Title 2
This is some description for Card 2.
<img src="image3.jpg" alt="Card Image 3">
Card Title 3
This is some description for Card 3.