Update header components. Update theme button.

components/settings/ThemeButton.js

@@ -1,6 +1,8 @@
 import React from 'react';
 import Button from 'components/common/Button';
 import useTheme from 'hooks/useTheme';
+import ToggleOn from 'assets/toggle-on.svg';
+import ToggleOff from 'assets/toggle-off.svg';
 
 export default function ThemeButton() {
   const [theme, setTheme] = useTheme();
@@ -9,5 +11,12 @@ export default function ThemeButton() {
     setTheme(theme === 'light' ? 'dark' : 'light');
   }
 
-  return <Button onClick={handleClick}>{theme}</Button>;
+  return (
+    <Button
+      icon={theme === 'light' ? <ToggleOff /> : <ToggleOn />}
+      size="large"
+      variant="light"
+      onClick={handleClick}
+    />
+  );
 }