Add <Overlay />

src/components/Overlay.js

@@ -0,0 +1,23 @@
+import React from 'react'
+
+export default ({
+  className = '',
+  color = 'var(--secondary)',
+  opacity = 0.2,
+  ...props
+}) => (
+  <div
+    className={`Overlay ${className}`}
+    style={{
+      color,
+      opacity,
+      backgroundColor: 'currentColor',
+      position: 'absolute',
+      left: 0,
+      right: 0,
+      top: 0,
+      bottom: 0
+    }}
+    {...props}
+  />
+)