div { border: thin red solid; margin: 1em; background: white}
[id]:before { background: yellow; content: "id: " attr(id) }
[class]:before { background: yellow; content: "class: " attr(class) ". " }
h1:before { background: yellow; content: "h1: " }
h2:before { background: yellow; content: "h2: " }
h3:before { background: yellow; content: "h3: " }
h4:before { background: yellow; content: "h4: " }

h1, h2, h3, h4, p { margin: 0 }
p span { display: none }
p:hover span { display: inline }