help/_scss/_toc.scss

.bd-toc {
    strong {
        display: block;
        padding: 1rem 1.5rem .5rem;
    }

    .section-nav {
        padding-left: 0;
    }

    .toc-entry {
        display: block;

        a {
            display: block;
            padding: .25rem 1.5rem;
            color: #77757a;

            &:hover {
                color: $link-color;
                text-decoration: none;
            }
        }

        &.toc-h3 {
            padding-left: 0.5rem;
        }
    }
}

.bd-toc-default {
    @supports (position: sticky) {
        position: sticky;
        top: 4rem;
        height: subtract(100vh, 4rem);
        overflow-y: auto;
    }

    order: 2;
    border-left: 1px solid #eee;
    padding: 0;
    @include font-size(.875rem);

    .toc-entry {
        a.active {
            color: $link-color;
        }
    }
}