feat: use the built-in dark mode by tailwind

src/main.postcss

@@ -2,21 +2,30 @@
 @import 'tailwindcss/components';
 @import 'tailwindcss/utilities';
 
-html, body, #app {
+html,
+body,
+#app {
   height: 100vh;
   width: 100vw;
   margin: 0;
   padding: 0;
 }
 
-.schema-dark {
+html.dark {
   background: #222;
 }
 
 .btn {
-  @apply px-4 py-1 rounded bg-teal-600 inline-block text-white cursor-pointer hover:bg-teal-700 disabled:cursor-default disabled:bg-gray-600 disabled:opacity-50;
+  @apply
+    px-4 py-1 rounded inline-block
+    bg-teal-600 text-white cursor-pointer
+    hover:bg-teal-700
+    disabled:cursor-default disabled:bg-gray-600 disabled:opacity-50;
 }
 
 .icon-btn {
-  @apply opacity-75 transition duration-200 ease-in-out cursor-pointer inline-block select-none hover:opacity-100;
+  @apply
+    inline-block cursor-pointer select-none
+    opacity-75 transition duration-200 ease-in-out
+    hover:opacity-100;
 }