Changed the dark mode color-bg-loading-panel to be a darker grey so it doesn't stick out as harshly from the background (#29)

package.json

@@ -1,7 +1,7 @@
 {
   "name": "@microsoft/azure-iot-ux-fluent-css",
   "description": "Azure IoT common styles library for CSS, Colors and Themes",
-  "version": "7.0.3",
+  "version": "7.0.4",
   "license": "MIT",
   "engines": {
     "node": "^8.0.0"

src/dark/_color.fluent.scss

@@ -197,7 +197,7 @@
     --color-hyperlink-disabled: var(--color-text-30);
 
     // Loading
-    --color-bg-loader-panel: var(--color-grey-20);
+    --color-bg-loader-panel: var(--color-grey-70);
     --color-bg-loader-spinner: var(--color-blue-10);
     --color-border-loader-global-segment: var(--color-blue-10);
     --color-border-loader-global-track: var(--color-grey-40);