Symfony doc, wide layout, no distractions.

symfony.com.user.css

/* ==UserStyle==
@name           symfony.com - 25/05/2020 à 15:29:45
@namespace      github.com/openstyles/stylus
@version        1.0.0
@description    A new userstyle
@author         Me
==/UserStyle== */
@-moz-document url-prefix("https://symfony.com/doc/") {
    .container {
        max-width: 100% !important;
    }

    .header__bottom {
        position: relative;
    }

    /* Make navi menu fixed and same color as background. */
    .doc__nav {
        position: fixed;
        top: 120px !important;
        background: var(--page-background);
        padding: 10px;
        border-radius: 5px;
        z-index: 1;
    }

    .doc__tools {
        position: fixed;
        left: 10px;
        top: 50px !important;
    }
    
    .version__all {
        right: auto;
    }

    /* Hide ads, conference dates, Symfony network, etc. */
    .header__top,
    [data-category="Ads"],
    .ads,
    #sln,
    .sfbook-banner,
    .conference-banner,
    .doc__backer,
    div.d-sm-block:nth-child(2) {
        display: none !important;
    }

    #content_wrapper {
        margin-top: 0;
    }
    
    aside{
        width: 15% !important;
    }
    
    main{
        width: 85% !important;
    }
}

Makes Symfony documentation use most of the page width, only leaving some space for the navigation menu on the left.
Hides most distractions like banners, sponsors, etc.
Uses the background color variable in order to preserve theme synchronization.