MediaWiki:Vector.css

/* HIDE all sidebar sections for anonymous users */
body:not(.mw-user-loggedin) #mw-panel .portal {
    display: none !important;
}

/* SHOW only the logo */
body:not(.mw-user-loggedin) #p-logo {
    display: block !important;
}

/* ENSURE logo image itself is visible */
body:not(.mw-user-loggedin) #p-logo a,
body:not(.mw-user-loggedin) #p-logo a img {
    display: block !important;
    visibility: visible !important;
}

/* SHOW personal tools (login link) */
body:not(.mw-user-loggedin) #p-personal {
    display: block !important;
}

/* OPTIONAL: Hide sidebar background (purely visual) */
body:not(.mw-user-loggedin) #mw-panel {
    background: none;
    padding-top: 0;
}

/* OPTIONAL: Center content area more nicely for anon */
body:not(.mw-user-loggedin) #content {
    margin-left: 0 !important;
}