Define typescript type for placeholders

client/placeholders/Square.tsx

@@ -1,6 +1,10 @@
 import React from 'react';
 
-const Square = ({ size = 8 }) => {
+interface SquareProps {
+    size?: number;
+}
+
+const Square: React.FC<SquareProps> = ({ size = 8 }) => {
     return (
         <div className="w-100 h-100 bg-black-30 br2" />
     );