html, body {
    max-width: 600px;
    margin: 0 auto;
}

img {
    width: 100%;
}

code.block {
    background-color: rgba(220, 220, 220, 0.534);
    padding: 10px;
    display: block;
    margin: 10px auto;
    border-radius: 5px;
}

pre {
    margin: 0;
    white-space: pre-wrap;       /* css-3 */
    white-space: -moz-pre-wrap;  /* Mozilla, since 1999 */
    white-space: -pre-wrap;      /* Opera 4-6 */
    white-space: -o-pre-wrap;    /* Opera 7 */
    word-wrap: break-word;       /* Internet Explorer 5.5+ */
}

@media only screen and (max-width: 600px) {
    html, body {
        margin: 5px;
    }
}