Remove all the unnecessary junk from the Outlook Web App and polish it a little

declutter-outlook.user.css

/* ==UserStyle==
@name           Declutter Outlook
@namespace      https://github.com/solarkraft
@version        1.0.2
@description    Remove all the unnecessary junk from the Outlook Web App and polish it a little
@author         solarkraft
==/UserStyle== */

@-moz-document domain("outlook.office.com") {
    #app > div > div:nth-child(2) {
        position: absolute;
        top: 0;
        left: 0;
        right: 0;
    }

    /* App switcher button */
    #O365_HeaderLeftRegion {
        display: none;
    }
    /* Logo */
    #Region_2 {
        display: none;
    }
    /* Those annoying unnecessary stuoid shortcuts to other apps */
    /*#headerButtonsRegionId {
      display: none;
    }*/
    #owaSearchBox_container {
        z-index: 1;
        /* margin-left: 22rem; */
        /* Ooops, we need to account for the menu when writing an E-Mail */
        margin-left: 100%;
    }
    /* Get search bar a bit more to the right */
    #owaNoteFeedButton_container {
        display: none;
    }

    #searchBoxColumnContainerId {
        height: 28px;
        margin-top: -2px
    }

    #searchBoxColumnContainerId > div:nth-of-type(1) {
        box-shadow: none;
        border: solid 1px #eee;
    }


    /* User menu */
    #O365_HeaderRightRegion {
        z-index: 1;
        background: transparent;

        position: relative;
        right: 26px;
        top: -6px
    }
    /* Hide avatar */
    #O365_MainLink_Me > div:nth-last-of-type(1) > div:nth-last-child(1) {
        display: none;
    }
    /* Hide avatar that appears after opening the menu (idk either) */
    #mectrl_headerPicture {
        display: none;
    }
    #O365_MainLink_Me {
        background: transparent;
    }

    /* User dropdown */
    #mectrl_main_body {
        transform: translateY(32px)
    }
    /* Keep background neutral when clicking */
    #mectrl_main_trigger:active,
    #mectrl_main_trigger:focus {
        background-color: transparent;
    }

    /* Keep buttons above search bar for edge cases */
    [data-focuszone-id="FocusZone11"] {
        position: relative;
        z-index: 2
    }

    /* Hide side bar */
    #LeftRail {
        display: none;
    }
    #app > div > div > div {
        flex-grow: 1
    }

    /* Make floating bar less ... floaty */
    #BottomBar > div:nth-child(1) {
        box-shadow: none;
        /* box-shadow: lightgrey 0 1px 2px; */
        border: solid 1px #eee;
    }

    /* Fix margin to search bar */
    #BottomBar {
        top: 2px;
    }
    /* Re-center ribbons */
    #TopBar {
        position: relative;
        top: 3px;
    }

    /* Calendar */
    /* Increase distance from now-lower floaty bar */
    #MainModule > div:nth-child(3) {
        position: relative;
        top: 3px;
    }
    /* Fix background that is now shown */
    #MainModule {
        background: var(--fallback-neutralLighterAlt);
    }
    /* Make calendar container less floaty */
    #MainModule > div:nth-child(3) > div > div {
        box-shadow: none !important;
        border: solid 1px #eee;
    }
}