body {
    line-height: 1.5;
    font-size: 0.8rem;
}

.boite {
    background-color: #ccc;
}

.box2 {
    margin: 2em;
}

.box3 {
    padding: 2em 1em;
}

.box4 {
    padding: 2em 1em;
    border: 2px solid red;
}

.box5 {
    margin: 2em;
    padding: 2em 1em;
    border: 2px solid red;
    width: 400px;
}

.box6 {
    margin: 2em;
    padding: 2em 1em;
    border: 2px solid red;
    width: 400px;
    box-sizing: border-box;
}