Use prefers-color-scheme for dark theme docs

docs/content/.vuepress/config.js

@@ -1,5 +1,6 @@
 module.exports = {
   title: 'PluralKit',
+  theme: 'default-prefers-color-scheme',
 
   base: "/",
   head: [

docs/package.json

@@ -14,5 +14,8 @@
     "vuepress": "^1.3.1",
     "vuepress-plugin-clean-urls": "^1.1.1",
     "vuepress-plugin-dehydrate": "^1.1.4"
+  },
+  "dependencies": {
+    "vuepress-theme-default-prefers-color-scheme": "^1.1.1"
   }
 }

docs/yarn.lock

@@ -2480,6 +2480,13 @@ 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"
@@ -7478,6 +7485,13 @@ vuepress-plugin-smooth-scroll@^0.0.3:
   dependencies:
     smoothscroll-polyfill "^0.4.3"
 
+vuepress-theme-default-prefers-color-scheme@^1.1.1:
+  version "1.1.1"
+  resolved "https://registry.yarnpkg.com/vuepress-theme-default-prefers-color-scheme/-/vuepress-theme-default-prefers-color-scheme-1.1.1.tgz#11389abba0f1c15f2dbea724e80b60937bda70f8"
+  integrity sha512-aLWYuFRk5EFcE4bAGzokAoOD92T/daodnZnuZnzF46jOl/ZtYHFV83uwXlbBUerdQE/IAxgtfuYRELXY5sUIKA==
+  dependencies:
+    css-prefers-color-scheme "^3.1.1"
+
 vuepress@^1.3.1:
   version "1.5.2"
   resolved "https://registry.yarnpkg.com/vuepress/-/vuepress-1.5.2.tgz#b79e84bfaade55ba3ddb59c3a937220913f0599b"