Add Dark mode support to docs

Author: marshallswain

docs/.vuepress/config.js

@@ -1,6 +1,7 @@
 module.exports = {
   title: 'FeathersVuex',
   description: 'Integration of FeathersJS, Vue, and Nuxt for the artisan developer',
+  theme: 'default-prefers-color-scheme',
   themeConfig: {
     repo: 'feathers-plus/feathers-vuex',
     docsDir: 'docs',

package.json

@@ -119,7 +119,8 @@
     "lodash.trim": "^4.5.1",
     "serialize-error": "^3.0.0",
     "sift": "^7.0.1",
-    "steal-typescript": "^0.5.0"
+    "steal-typescript": "^0.5.0",
+    "vuepress-theme-default-prefers-color-scheme": "^1.0.3"
   },
   "devDependencies": {
     "@feathersjs/authentication-client": "^1.0.11",

yarn.lock

@@ -3697,6 +3697,13 @@ css-parse@~2.0.0:
   dependencies:
     css "^2.0.0"
 
+css-prefers-color-scheme@^3.1.1:
+  version "3.1.1"
+  resolved "https://registry.yarnpkg.com/css-prefers-color-scheme/-/css-prefers-color-scheme-3.1.1.tgz#6f830a2714199d4f0d0d0bb8a27916ed65cff1f4"
+  integrity sha512-MTu6+tMs9S3EUqzmqLXEcgNRbNkkD/TGFvowpeoWJn5Vfq7FMgsmRQs9X5NXAURiOBmOxm/lLjsDNXDE6k9bhg==
+  dependencies:
+    postcss "^7.0.5"
+
 css-select-base-adapter@^0.1.1:
   version "0.1.1"
   resolved "https://registry.yarnpkg.com/css-select-base-adapter/-/css-select-base-adapter-0.1.1.tgz#3b2ff4972cc362ab88561507a95408a1432135d7"
@@ -11208,6 +11215,13 @@ vuepress-plugin-smooth-scroll@^0.0.3:
   dependencies:
     smoothscroll-polyfill "^0.4.3"
 
+vuepress-theme-default-prefers-color-scheme@^1.0.3:
+  version "1.0.3"
+  resolved "https://registry.yarnpkg.com/vuepress-theme-default-prefers-color-scheme/-/vuepress-theme-default-prefers-color-scheme-1.0.3.tgz#85d5872a05b2cdc9ff3d22ba24380699f60fd3ad"
+  integrity sha512-CNu+opm+yvdObtzhxa2Mm4d3Ho9aM3NM17RKFpJ77soXeNX7muox+npKTSZiZwY685CFgFAJpSTm01/2f3aPCA==
+  dependencies:
+    css-prefers-color-scheme "^3.1.1"
+
 vuepress@^1.0.2:
   version "1.2.0"
   resolved "https://registry.yarnpkg.com/vuepress/-/vuepress-1.2.0.tgz#2f2cdf337ad40a3e4866dfd33e97b840db386af7"