body {
    counter-reset: travail;
    margin: auto;
    line-height: 1.3em;
    text-align: justify;
    width: 800px;
}


h1 {
    text-align: center;
    line-height: 2em;
    padding-top:1.3em;
    letter-spacing: 0.05em;
}

h1 {
    margin-left: auto;
    margin-right: auto;
}

header p {
    width: 100%;
    text-align: center;
}

h2 {
    counter-increment: travail;
    counter-reset: subpart;
    padding-top: 1.3em;
}

h2:before {
    content: counter(travail)". ";
}

h3 {
    padding-top: 1.3em;
}

h3:before {
    counter-increment: subpart;
    content: counter(travail)". "
        counter(subpart)" ";
}