Update _dark.scss

Author: koraxial

_sass/yat/_dark.scss

@@ -51,6 +51,11 @@ html[data-theme="dark"]  {
     background-image: url('https://raw.githubusercontent.com/ps2wiki/ps2wiki.github.io/refs/heads/upstream/assets/xmas/xmas_bg_dark.png');
     background-position: no-repeat;
     background-size: cover;
+}
+.holi {
+    background-image: url('https://raw.githubusercontent.com/ps2wiki/ps2wiki.github.io/refs/heads/upstream/assets/themes/holi/background.png');
+    background-position: no-repeat;
+    background-size: cover;
 }
   .site-header {
     background-color: #090909;