fix a less reference error

customize.dist/src/less2/include/colortheme-dark.less

@@ -31,6 +31,17 @@
 @cryptpad_color_brand_fader: fade(@cryptpad_color_brand, 50%);
 @cryptpad_color_brand_fadest: fade(@cryptpad_color_brand, 25%);
 
+// XXX this whole block was copy-pasted from colortheme.less to avoid a reference error --ansuz
+@cryptpad_color_hint_grey: #777;
+@cryptpad_color_dark_grey: #999999;
+@cryptpad_color_neutral_grey: #aaaaaa;
+@cryptpad_color_neutral2_grey: #cccccc;
+@cryptpad_color_help_grey: #dddddd;
+@cryptpad_color_grey: #e0e0e0;
+@cryptpad_color_toolbar_grey: #EEEEEE;
+@cryptpad_color_light_grey: #f1f1f1;
+@cryptpad_color_lighter_grey: #f9f9f9;
+
 @cryptpad_color_white: #FFF;
 @cryptpad_color_grey_50: #FAFAFA;
 @cryptpad_color_grey_100: #F5F5F5;