docs: Reword comparison between React authoring and CSS authoring

This sentence contrasts authoring React with authoring CSS. The previous version did this in a way that makes the React authoring seem like a more advanced activity (“actual (…) code”), and authoring CSS the less advanced (described as “playing with”). The rewording tries to address that.

website/docs/swizzling.mdx

@@ -8,7 +8,7 @@ In this section, we will introduce how customization of layout is done in Docusa
 
 > Déja vu...?
 
-This section is similar to [Styling and Layout](./styling-layout.mdx), but this time, we will write actual React code instead of playing with stylesheets. We will talk about a central concept in Docusaurus: **swizzling**, which allows **deeper site customizations**.
+This section is similar to [Styling and Layout](./styling-layout.mdx), but this time, we will customize React components themselves, rather than what they look like. We will talk about a central concept in Docusaurus: **swizzling**, which allows **deeper site customizations**.
 
 In practice, swizzling permits to **swap a theme component with your own implementation**, and it comes in 2 patterns: