docs/source/_static/scss/includes/_toc.scss

#table-of-contents {
    display: none;
}

.content__toc {
    position: sticky;
    top: 0;

    @include breakpoint-min(breakpoints(lg)) {
        flex-shrink: 0;
        order: 2;
        width: 14rem;
        height: 100vh;
        padding: var(--content-padding) var(--content-padding) var(--content-padding) 0;
        overflow-y: auto;

        .icon {
            display: none;
        }
    }

    @include breakpoint-max(breakpoints(lg)) {
        display: flex;
        align-items: center;
        padding: var(--content-padding);
        background-color: var(--body-bg);
        z-index: $z-index-header - 2;
    }

    .icon {
        height: 2.7rem;
        width: 2.7rem;
        padding: 0.75rem;
        border: 1px solid var(--theme-light-bg);
        cursor: pointer;
    }

    &.active {
        & > .content__toc__inner {
            & > ul {
                display: block;
            }
    
            h3 > a {
                border-radius: $border-radius $border-radius 0 0;
    
                &:after {
                    transform: rotate(180deg);
                }
            }
        }
    }
}

.content__toc__inner {
    @include breakpoint-max(breakpoints(lg)) {
        position: relative;
        display: flex;
        align-items: center;
        flex: 1;
        margin: 0 0.75rem;

        & > h3 {
            flex: 1;
        }
    }

    h3 {
        margin: 0;
        line-height: 1;

        & > a {
            font-size: 1rem;
            color: var(--headings-color);
            font-size: 0;

            &:before {
                content: "Contents";
                font-size: 1rem;
            }

            @include breakpoint-max(breakpoints(lg)) {
                padding: 0.85rem;
                background-color: var(--theme-light-bg);
                border-radius: $border-radius;
                display: block;
                position: relative;

                &:after {
                    content: "";
                    height: 1rem;
                    width: 1rem;
                    position: absolute;
                    right: 1.25rem;
                    top: 0.9rem;
                    background: var(--toc-caret-icon) no-repeat center;
                    background-size: 1rem;
                    transform-origin: center;
                }
            }
        }
    }

    ul {
        margin: 0;
        padding: 0;
        list-style: none;
        font-size: $font-size-sm;

        ul ul {
            margin-left: 1rem;
        }
    }

    & > ul {
        @include breakpoint-min(breakpoints(lg)) {
            position: relative;
            padding-left: 1rem;
            margin-top: 1rem;
        
            &:before {
                content: "";
                width: 2px;
                height: calc(100% - 0.8rem);
                position: absolute;
                left: 0;
                top: 0.5rem;
                background-color: var(--theme-light-bg);
            }
        }

        @include breakpoint-max(breakpoints(lg)) {
            position: absolute;
            left: 0;
            top: 100%;
            width: 100%;
            background-color: var(--theme-light-bg);
            display: none;
            border-radius: 0 0 $border-radius $border-radius;
            z-index: 1;
            border-top: 1px solid var(--theme-light-hover-bg);
            padding: 0.65rem 1rem 1rem;
            max-height: 12rem;
            overflow-y: auto;
        }

        & > li {
            & > a {
                font-size: 0;

                &:before {
                    content: "Introduction";
                    font-size: $font-size-sm;
                    transition: color 300ms;
                }
            }

            a {
                display: block;
                color: var(--text-muted-color);
                code {
                    display: none;
                }

                &:hover {
                    color: var(--text-color);
                }
            }

            & > ul {
                & > li {
                    a {
                        transition: color 300ms;
                        margin: 0.25rem 0;
                        position: relative;

                        &:before {
                            content: "";
                            width: 2px;
                            height: calc(100% - 0.8rem);
                            position: absolute;
                            left: 0;
                            top: 0.5rem;
                            
                        }
                    }
                }
            }
        }
    }
}