add enable/disable checkbox, and heading modifier

src/shared/Checkbox.js

@@ -0,0 +1,19 @@
+import React from 'react';
+
+const Checkbox = ({ checked, onChange }) => {
+  return (
+    <div className="bg-white border-2 rounded border-gray-400 hover:border-gray-500 w-8 h-8 flex flex-shrink-0 justify-center items-center mr-2 focus-within:border-blue-500 cursor-pointer">
+      <input
+        type="checkbox"
+        className="w-8 h-8 opacity-0 absolute cursor-pointer"
+        checked={checked}
+        onChange={e => onChange(e.target.checked)}
+      />
+      <i className="material-icons fill-current hidden text-lg font-bold text-gray-800 cursor-pointer">
+        check
+      </i>
+    </div>
+  );
+};
+
+export default Checkbox;