Add Dark Mode Support for Global CSS

src/styles.scss

@@ -13,6 +13,18 @@
   --motion-duration-multiplier: 0 !important;
 }
 
+html.dark-theme {
+  color: white;
+
+  & > body {
+    background-color: oklch(0.1776 0 0);
+  }
+
+  section.feature-block {
+    background-color: oklch(0 0 0 / 60%);
+  }
+}
+
 body {
   font-family: 'NanumSquareNeo', 'Wanted Sans Variable', 'Pretendard JP', sans-serif;
   font-weight: 500;