feat: add empty page color support with new CSS file and update index.html

public/colors.css

@@ -0,0 +1,9 @@
+@media (prefers-color-scheme: dark) {
+  html > body { background: #101828; color: #e5e7eb; }
+  html:not(.dark) > body { background: #f3f4f6; color: black; }
+}
+
+@media (prefers-color-scheme: light) {
+  html > body { background: #f3f4f6; color: black; }
+  html.dark > body { background: #101828; color: #e5e7eb; }
+}