A custom version of https://userstyles.org/styles/31267/global-dark-style-changes-everything-to-dark made to look like the Darcula Theme known from Jetbrains IDEs

Darcula.user.css

/* ==UserStyle==
@name           Darcula
@namespace      github.com/openstyles/stylus
@version        1.0.0
@description    A new userstyle
@author         OmegaRogue
==/UserStyle== */
@-moz-document url-prefix("ftp://"),
url-prefix("file://"),
url-prefix("about"),
url-prefix("javascript"),
regexp("https?://(?!(www.twitch.tv)).*"), regexp("")
{
    /* Insert code here... */
    html
    {
        background: /***** COPY AND PASTE THE URL OF YOUR BACKROUND-IMAGE INSIDE THE url("") *****/
        /***** FOR A SIMPLE BLACK BACKGROUND JUST REMOVE THE URL LINE ABOVE *****/
        /***** Some background-images (you can also use your own url):

  default:      https://abload.de/img/bg_digital94uzx.png
  old default1: https://abload.de/img/b1fgs11.png
  old default2: https://abload.de/img/ultra_x2vm9k.jpg
                https://abload.de/img/b2w4shd.png
                https://abload.de/img/b3qrs99.png
                https://abload.de/img/b4zcse8.png
                https://abload.de/img/b5b1s7x.png
                https://abload.de/img/b6umsmy.png
                https://abload.de/img/b7ars8c.png
                https://abload.de/img/kubrickbgcolor2darkr8skc.png
                https://abload.de/img/xpattern_darkq8s3i.png
                https://abload.de/img/mainpatternolxcq.png

*/
        #2B2B2B/* fixed */
        !important
    }



    /*----- DEFAULT TEXT, BORDER & BACKGROUND COLORS -----*/
    *
    {
        color: #A9B7C6 !important;
        text-shadow: none !important;
        box-shadow: none !important;
        background-color: transparent !important;
        border-color: #444 !important;
        border-top-color: #444 !important;
        border-bottom-color: #444 !important;
        border-left-color: #444 !important;
        border-right-color: #444 !important
    }

    /*  div:not([id*="code"]):not([id*="Code"]){
      background-color: rgba(42,42,42, 0.2) !important;
      border-color: #000000 !important;
      border-width: thin !important;
    } */
    body
    {
        background: transparent !important
    }


    *:before,
    *:after
    {
        background-color: transparent !important;
        border-color: #444 !important
    }


    a,
    a *
    {
        color: #A9B7C6 !important;
        
        text-decoration: none !important
    }

    a:link *
    {
        color: #BED6FF !important;
        text-decoration: none !important
    }
    
     [class*=section],
    section *,
    [class*=code]
    {
        background-color: #2B2B2B !important;
    }

    a:hover,
    a:hover *,
    a:visited:hover,
    a:visited:hover *,
    span[onclick]:hover,
    div[onclick]:hover,
    [role="link"]:hover,
    [role="link"]:hover *,
    [role="button"]:hover *,
    [role="menuitem"]:hover,
    [role="menuitem"]:hover *,
    .link:hover,
    .link:hover *
    {
        color: #BED6FF !important;
        text-shadow: 0 0 5px rgba(255, 255, 200, 0.9) !important;
        background-color: #323232 !important;
    }

    .minibutton,
    .button,
    .btn,
    a[class*="btn"]:visited
    {
        color: #9876AA !important;
        background-image: none !important;
    }

    a:visited,
    a:visited *
    {
        color: #607069 !important
    }

    a.highlight,
    a.highlight *,
    a.active,
    a.active *,
    .selected,
    .selected *,
    [href="#"]
    {
        color: #A9B7C6 !important;
        font-weight: bold !important;
        background-color: #4b4f51 !important;
    }

    h1,
    h2,
    h3,
    h4,
    h5,
    h6,
    h1 *,
    h2 *,
    h3 *,
    strong,
    [id*="headline"],
    [class*="headline"],
    [id*="header"],
    [class*="header"],
    [class*="header"] td
    {
        color: #CB772F !important
    }

    a h1,
    a h2,
    a h3,
    a h4,
    a h5,
    a h6,
    h1 a,
    h2 a,
    h3 a,
    a strong,
    a[id*="headline"],
    a[class*="headline"],
    a[id*="header"],
    a[class*="header"]
    {
        text-decoration: underline !important
    }

    [class*="error"],
    [class*="alert"],
    code,
    span[onclick],
    div[onclick]
    {
        color: #D25252 !important
    }

    ::-moz-selection
    {
        background: #377 !important;
        color: #000 !important
    }

    ::selection
    {
        background: #377 !important;
        color: #000 !important
    }

    :focus
    {
        outline: none !important;
        background-color: #323232 !important
    }



    /*----- MENU & CO BACKGROUND-COLORS -----*/
    div[style="display: block;"],
    div[role="navigation"]
    {
        background: rgba(0, 0, 0, .5) !important
    }

    table
    {
        background: rgba(40, 30, 30, .6) !important;
        border-radius: 6px !important
    }

    table > tbody > tr:nth-child(even),
    table > tbody > tr > td:nth-child(even)
    {
        background-color: rgba(0, 0, 0, .2) !important
    }

    iframe,
    embed,
    nav,
    label [onclick],
    nav ul,
    div[style*="position:"][style*="left:"][style*="visible"],
    div[style*="z-index:"][style*="left:"][style*="visible"],
    div[style*="-moz-user-select"],
    div[role="menu"],
    div[role="dialog"],
    span[class*="script"] div,
    [id*="menu"],
    [id*="Menu"],
    [class*="select-menu"],
    [role*="listbox"],
    [id*="navigation"],
    [class*="popover"],
    [class*="dropdown"],
    [class*="popup"],
    [class="title"],
    ul[style*="display:"],
    ul[style*="visibility:"] ul,
    [id*="nav"] ul,
    [class*="nav"] ul,
    ul[class*="menu"],
    a[onclick][style*="display"],
    a[id*="ghosteryfirefox"],
    #ghostery-purple-bubble,
    #translator-popup,
    .menu,
    .tooltip,
    .hovercard,
    .vbmenu_popup
    {
        background: #3c3f41 !important;
        border-radius: 5px !important;
        box-shadow: 1px 1px 5px #000 !important;
        border-width: thin !important;
    }

    header,
    #header,
    footer,
    #footer
    {
        background: rgba(49, 51, 53, .9) !important;
        box-shadow: 0 0 5px #000 !important
    }

    body > #dialog,
    body > .xenOverlay
    {
        background: rgba(19, 19, 19, .96) !important;
        background-clip: padding-box !important;
        box-shadow: 0 0 15px #000, inset 0 0 0 1px rgba(200, 200, 200, .5), inset 0 0 5px #111 !important;
        border: 10px solid rgba(99, 99, 99, .7) !important;
        border-radius: 0 !important;
    }

    [id*="overlay"],
    [id*="lightbox"],
    blockquote
    {
        background-color: rgba(35, 35, 35, .9) !important;
        border-radius: 5px
    }

    pre,
    dl,
    .Message code
    {
        background-color: rgba(5, 5, 5, .5) !important
    }

    [class*="tooltipster-base"]
    {
        border-color: #BED6FF !important;
        background-color: #323232 !important;
    }

    /*----- DEFAULT BUTTONS, SEARCHBOXES & CO -----*/
    input,
    select,
    button,
    [role="button"],
    a.button,
    a.submit,
    a.BigButton,
    a.TabLink,
    .install[onclick]
    {
        -moz-appearance: none !important;
        -webkit-appearance: none !important;
        transition: border-color 0.3s !important;
        background: #323232 !important;
        color: #9876AA !important;
        text-shadow: 0 1px #000 !important;
        border: 2px solid #333 !important;
        border-radius: 4px !important;
        box-shadow: 0 0 2px rgba(0, 0, 0, .9) !important
    }

    a[href="javascript:;"],
    a[class*="button"]:not(:empty),
    a[id*="button"]:not(:empty),
    a[id*="Button"]:not(:empty),
    div[class*="button"][onclick]
    {
        transition: border-color 0.3s !important;
        background: #3c3f41 !important;
        color: #adadad!important;
        text-shadow: 0 1px #000 !important;
        border-color: #333 !important;
        box-shadow: 0 0 2px rgba(0, 0, 0, .9) !important
    }

    a[href="javascript:;"]:hover,
    a[class*="button"]:not(:empty):hover,
    a[id*="button"]:hover,
    a[id*="Button"]:not(:empty):hover,
    div[class*="button"][onclick]:hover
    {
        background-color: #4b4f51 !important;
        color: #adadad !important;
        border: 2px solid #555 !important;
    }

    input *,
    select *,
    button *,
    a.button *,
    a.submit *
    {
        color: #BED6FF !important;
        text-shadow: none !important;
        border: 2px solid #555 !important;
    }

    input:hover,
    input[type="button"]:hover,
    select:hover,
    button:hover,
    [role="button"]:hover,
    a.button:hover,
    a.submit:hover,
    a.BigButton:hover,
    a.TabLink:hover,
    [role="option"]:hover
    {
        border: 2px solid #555 !important;
        border-top-color: #555 !important;
        border-bottom-color: #555 !important;
        border-left-color: #555 !important;
        border-right-color: #555 !important
    }

    input:focus,
    select:focus
    {
        box-shadow: 0 0 5px #077 !important
    }

    input *:hover *
    {
        color: #F0F0F0 !important;
        text-shadow: 0 0 2px #FFF !important
    }

    input[disabled],
    select[disabled],
    button[disabled],
    input[disabled]:hover,
    select[disabled]:hover,
    button[disabled]:hover,
    input[disabled]:focus,
    select[disabled]:focus,
    button[disabled]:focus
    {
        opacity: 0.5 !important;
        border-color: #333 !important
    }

    /*
input[type="checkbox"], input[type="radio"] {
    box-shadow: 0 0 0 2px #444, 0 0 2px 2px #000 !important;
    opacity: 0.7;
    transition: box-shadow 0.2s, opacity 0.2s !important}
input[type="checkbox"]:not([disabled]):hover, input[type="radio"]:not([disabled]):hover {
    opacity: 0.9}
input[type="checkbox"]:not([disabled]):active, input[type="radio"]:not([disabled]):active {
    box-shadow: 0 0 0 2px #999, 0 0 2px 2px #000 !important}
input[type="checkbox"]:checked, input[type="radio"]:checked {
    box-shadow: 0 0 0 2px #077, 0 0 2px 2px #000 !important}
input[type="checkbox"][disabled], input[type="radio"][disabled] {
    opacity: 0.35}
*/
    input[type="checkbox"]
    {
        border-radius: 1px !important
    }

    input[type="radio"],
    input[type="radio"]:focus
    {
        border-radius: 100% !important
    }

    input[type="checkbox"],
    input[type="radio"]
    {
        min-width: 12px;
        min-height: 12px
    }

    input[type="checkbox"]:checked,
    input[type="radio"]:checked
    {
        border-color: #077 !important;
        box-shadow: 0 0 5px #077 !important
    }

    select
    {
        padding-right: 15px !important;
        background: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAcAAAAECAYAAABCxiV9AAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsMAAA7DAcdvqGQAAAAeSURBVBhXY5g5c+Z/BiwALo6uAEMDTACXSWgSDAwA4jATh950E30AAAAASUVORK5CYII=) no-repeat right 4px center #060606 !important;
        transition: border-color 0.3s, background-position 0.3s !important
    }

    button:active,
    input[type="submit"]:active,
    input[type="button"]:active,
    a.button:active,
    a[class*="button"]:not(:empty):active,
    a.submit:active,
    a.BigButton:active,
    a.TabLink:active,
    .Active .TabLink
    {
        background: #292929 !important;
        color: #FFF !important
    }

    textarea
    {
        -moz-appearance: none !important;
        -webkit-appearance: none !important;
        background: rgba(0, 0, 0, .3) !important;
        border-radius: 3px !important;
        border: 1px solid #000 !important;
        box-shadow: inset 0 0 8px #000 !important;
        transition: border-color, background, 0.3s !important
    }

    textarea,
    textarea *
    {
        color: #C8C8C8 !important;
        text-shadow: 0 0 1px gray !important
    }

    textarea:hover,
    textarea:focus:hover
    {
        border-color: #333 !important
    }

    textarea:focus
    {
        background: rgba(0, 0, 0, .5) !important;
        border-color: #222 !important
    }

    textarea:focus,
    textarea:focus > *
    {
        text-shadow: none !important;
        box-shadow: none !important
    }

    option,
    optgroup
    {
        -moz-appearance: none !important;
        -webkit-appearance: none !important;
        background: none !important;
        color: #666 !important
    }

    optgroup
    {
        background: #222 !important;
        color: #DDD !important
    }

    option:not([disabled]):hover,
    option:focus,
    option:checked
    {
        background: linear-gradient(#333, #292929) !important;
        color: #DDD !important
    }

    /*----- IMAGE CHANGES -----*/
    body,
    *:not(:empty):not(html):not(span):not(a):not(b):not(option):not(select):not(img):not([style="display: block;"]):not([onclick*="open"]):not([onclick*="s_objectID"]):not([class*="stars"]):not([id*="stars"]):not([id="rating"]):not([class="rating"]):not([class*="SPRITE"]):not([id*="SPRITE"]):not([class*="item"]):not([id*="item"]):not([class*="thumb"]):not([class*="icon"]):not([class*="photo"]):not(.view):not(.text):not([id*="lbImage"]):not([class*="cc-in"]):not([class*="gr-body"]):not([id*="watch"]):not(#globalsearch):not([style*="background-image: url("]),
    .r3_hm,
    .gmbutton2 b,
    .gtab-i,
    .ph,
    .bstab-iLft,
    .csb,
    #pagination div,
    [style*="sprite2.png"],
    #mw-head-base,
    #mw-page-base
    {
        background-image: none !important
    }

    img
    {
        opacity: .7 !important;
        transition: opacity .2s
    }

    img:hover,
    a:hover img,
    #mpiv-popup
    {
        opacity: 1 !important
    }
}