Add project files.

ConstructorAppUI/wwwroot/AdminTheme/build/scss/_mixins.scss

@@ -0,0 +1,17 @@
+//
+// General: Mixins
+//
+
+@import "mixins/animations";
+@import "mixins/scrollbar";
+@import "mixins/cards";
+@import "mixins/sidebar";
+@import "mixins/navbar";
+@import "mixins/accent";
+@import "mixins/custom-forms";
+@import "mixins/backgrounds";
+@import "mixins/dark-mode";
+@import "mixins/direct-chat";
+@import "mixins/toasts";
+@import "mixins/touch-support";
+@import "mixins/miscellaneous";