html {
    margin: 0;
    font-family: Arial, Helvetica, sans-serif;
    font-size: 1.1em;
    line-height: 1em;
}
h1, h2, h3, h4 {
    text-align: center;
}
h2 {
    margin-top: 10%;
}
h4 {
    font-size: 1.1em;
    font-weight: normal;
    margin-bottom: 1%;
    border-bottom: 1px #222 solid;
}
p, h4, ol, ul {
    margin-left: 20%;
    margin-right: 20%;
}
img {
    display: block;
    width: 90%;
    max-width: 800px;
    margin-left: auto;
    margin-right: auto;
    margin-bottom: 10%;
    border: 20px #222 solid;
    border-radius: 20px;
}
@media (min-width: 640px) and (max-width: 900px) {
    h4 {
        margin-bottom: 3%;
    }
    p, h4, ol, ul {
        margin-left: 10%;
        margin-right: 10%;
    }
}
@media (max-width: 640px) {
    h1, h2 {
        line-height: 1.2em;
    }
    h4 {
        margin-bottom: 2%;
    }
    p, h4, ol, ul {
        margin-left: 5%;
        margin-right: 5%;
    }
    img {
        display: block;
        width: 95%;
        border: 0;
    }
}