zacharybillman-hugo/assets/css/extended/custom.css

.marginnote,
.sidenote {
    font-size: 80%;
    position: relative;
}
/* Wide viewport */
@media (min-width: 1080px) {
    .marginnote,
    .sidenote {
        float: right;
        clear: right;
        margin-right: -23vw;
        text-align: left;

        top: -3rem;
        width: 20vw;
        margin-top: 1rem;
    }
}

/* Narrow viewport */
@media (max-width: 1080px) {
    .marginnote,
    .sidenote {
        float: right;
        text-align: left;

        width: 100%;
        margin: 1rem 0;
        padding-left: 7.5%;
    }
}

/* Sidenote counter */
body {
    counter-reset: sidenote-counter;
}
.sidenote-number {
    counter-increment: sidenote-counter;
}
/* Counter before the sidenote in the margin. */
.sidenote::before {
    content: counter(sidenote-counter)".";
    position: relative;
    vertical-align: baseline;
    font-size: 0.9em;
    font-weight: bold;
}
/* Counter in the main body. */
.sidenote-number::after {
    content: counter(sidenote-counter);
    vertical-align: super;
    font-size: 0.7em;
    font-weight: bold;
    margin-right: 0.5rem;
}