Add Zen mode for distraction free drawing (#1450)

src/components/FixedSideContainer.tsx

@@ -5,14 +5,18 @@ import React from "react";
 type FixedSideContainerProps = {
   children: React.ReactNode;
   side: "top" | "left" | "right";
+  className?: string;
 };
 
 export function FixedSideContainer({
   children,
   side,
+  className,
 }: FixedSideContainerProps) {
   return (
-    <div className={`FixedSideContainer FixedSideContainer_side_${side}`}>
+    <div
+      className={`FixedSideContainer FixedSideContainer_side_${side} ${className}`}
+    >
       {children}
     </div>
   );