A stylesheet that de-clutters fandom.com and makes it nicer to read in large windows.

fandom_userstyle.css

.fandom-sticky-header {
    /* Make the thin header always visible. */
    transform: translateY(100%) !important;
    
    /* Remove space left by hiding global navigation. */
    left: 0px !important;
}

/* Make space for the sticky header including the original page margin. */
.page {
    margin-top: calc(46px + 12px) !important;
}

/* Add a radius to the right side since the right rail is always hidden. */
.page__main {
    border-radius: 3px !important;
}

/* Remove space left by hiding global navigation. */
.main-container {
    margin-left: 0px !important;
    width: 100% !important;
}

/* Remove space left by hiding global navigation. */
.search-modal::before {
    left: 0 !important;
}

/* Hide a bunch of elements. */
#WikiaBar,
#mixed-content-footer,
.wds-global-footer,
.global-footer,
.top-ads-container,
.bottom-ads-container,
.community-header-wrapper,
.global-navigation,
.page__right-rail,
.fandom-community-header__background {
    display: none !important;
}

/* Simulate page always being expanded. */
@media only screen and (min-width: 1280px) {
    /* Make space for the sticky header without the original page margin. */
    .page {
        margin-top: 46px !important;
    }

    .resizable-container {
        max-width: none !important;
        width: calc(100% - 240px) !important;
        margin: 0 0 0 240px !important;
    }
    
    .page__main,
    .sticky-toc.toc {
        border-radius: 0 !important;
    }
}

/* Make the maint content use the entire height */
@media only screen and (min-width: 1280px) {
    .page {
        display: flex !important;
    }
    
    .resizable-container,
    .page,
    .page__main {
        flex: 1 !important;
    }

    html,
    body,
    .main-container {
        height: 100% !important;
    }
}

/* ---------------------------------------------------------- */

/* Permanently show the sticky ToC as a left rail/sidebar. */
@media only screen and (min-width: 1280px) {
    /* Reset ToC containers */
    .page-side-tools__wrapper {
        height: unset !important;
        padding: unset !important;
        
        position: unset !important;
        left: unset !important;
        top: unset !important;
        transform: unset !important;
    }

    .page-side-tools {
        position: unset !important;
        top: unset !important;
    }

    .sticky-toc-wrapper {
        position: unset !important;
    }
    
    .sticky-toc.toc {
        width: unset !important;
        max-width: unset !important;
        margin: unset !important;

        position: unset !important;
        left: unset !important;

        box-shadow: unset !important;
    }
    
    .sticky-toc.toc > ul {
        max-height: unset !important;
    }

    /* ---------------------------------------------------------- */
    
    /* Necessary for the ul to have a scrollbar. */
    .page-side-tools,
    .sticky-toc-wrapper,
    .sticky-toc.toc {
        height: 100% !important;
    }

    .page-side-tools__wrapper {
        position: fixed !important;
        left: 0px !important;

        /* Make space for the sticky header. */
        top: 46px !important;

        width: 240px !important;
        /* Account for sticky header's height. */
        height: calc(100% - 46px) !important;
        
        border-right: 1px solid var(--theme-border-color);
        
        /* 
        .sticky-toc.toc sets this too, but that element loads slowly upon refresh. 
        Also, it may not always exist.
        */
        background: var(--theme-page-background-color--secondary);
    }

    .page-side-tool /* Hide tool buttons on the left side. */,
    .sticky-toc-close /* Hide close button for sticky ToC. */,
    #toc /* Hide the body's ToC cause the sticky one is shown. */ {
        display: none !important;
    }
    
    /* For proper overflow (https://stackoverflow.com/a/61844861) */
    .sticky-toc.toc {
        /* Always show the ToC. */
        display: flex !important;
        flex-direction: column;
    }
    
    .sticky-toc.toc > :not(ul) {
        flex-shrink: 0;
    }

    .sticky-toc.toc > ul {
        flex-grow: 1;
        overflow: auto !important;
        
        /*
        Disable the background. It's meant to add a shadow to the
        top and bottom edges, but it's broken for the bottom when
        the list is not the full height of the container.
        */
        background: none !important;
    }
}

/* ---------------------------------------------------------- */

.unified-search__layout {
    grid-template-areas: "left left main main main main main main main main main main" !important;
}

.unified-search__layout__right-rail {
    display: none !important;
}

@media only screen and (min-width: 1280px) {
    .unified-search__layout__left-rail {
        position: fixed !important;
        z-index: 200;
        left: 0px !important;

        /* Make space for the sticky header. */
        top: 46px !important;

        width: 240px !important;
        /* Account for sticky header's height. */
        height: calc(100% - 46px) !important;
    }
    
    .unified-search__layout {
        grid-template-areas: "main main main main main main main main main main main main" !important;
    }
}