* {
    margin: 0;
    box-sizing: border-box;
        /* don’t add padding to width and height */
}

html {
    font-size: 100%;
}

body {
    font-family: sans-serif;
    font-size: 1em;
}

.address-book{
    width: 25rem;
    height: 35rem;
    border: 2px solid black;
    margin: auto;
    overflow: scroll;
    resize: both;
}

dl {
    font-weight: bold;
    line-height: 2.25;
}

.address-book dt{
    background-color: darkblue;
    color: yellow;
    padding-left: 1rem;
    padding-right: 1rem;
    position: -webkit-sticky;
    position: sticky;
    top: 0;
}

.address-book dd{
    padding-left: 1rem;
    padding-right: 1rem;
    white-space: nowrap;
    border: 1px solid grey;
}