/* ⭐️ universal box-sizing */
*, *::before, *::after {
box-sizing: border-box;
}
body {
margin: 1em;
}
.fixed-width {
width: 400px;
padding: 1em;
}
summary {
background-color: tomato;
}
p {
background-color: lawngreen;
margin: 0;
}
.reference {
margin-top: 1em;
background-color: deepskyblue;
}