To make your dashboard theme to be dark, please go to quixnav.js file and make sure version: "dark"

        (function($) {
            "use strict"

            new quixSettings({
                version: "light", //2 options "light" and "dark"
                layout: "vertical", //2 options, "vertical" and "horizontal"
                navheaderBg: "color_1", //have 10 options, "color_1" to "color_10"
                headerBg: "color_1", //have 10 options, "color_1" to "color_10"
                sidebarStyle: "full", //defines how sidebar should look like, options are: "full", "compact", "mini" and "overlay". If layout is "horizontal", sidebarStyle won't take "overlay" argument anymore, this will turn into "full" automatically!
                sidebarBg: "color_1", //have 10 options, "color_1" to "color_10"
                sidebarPosition: "static", //have two options, "static" and "fixed"
                headerPosition: "static", //have two options, "static" and "fixed"
                containerLayout: "wide",  //"boxed" and  "wide". If layout "vertical" and containerLayout "boxed", sidebarStyle will automatically turn into "overlay".
                direction: "ltr" //"ltr" = Left to Right; "rtl" = Right to Left