wrong variable name when setting the theme

https://github.com/ChinmayMhatre/DarkMode-Blog/blob/e872b4cd52045fa50f4ac6b82c9402d518035aa6/component/Button.tsx#L13

The name of this variable should be `currentTheme` instead of `theme`, I think it's a small typo otherwise the default value of theme remain as `system`.

Open component/Button.tsx at the referenced line and inspect how the theme variable is used when setting the theme. Verify the naming matches the intended currentTheme value and confirm the default theme no longer remains system unexpectedly.

Written by the indexing model from the issue text.