a.footnote-ref::before {
    content: '[';
}

a.footnote-ref::after {
    content: ']';
}

/* https://discourse.gohugo.io/t/footnote-styling/114/6 */
sup, sub {
    vertical-align: baseline;
    position: relative;
    top: -0.4em;
}

sub {
    top: 0.4em;
}