Readapt the misuse of BEM, Code organization

- -- is only for a modifier, not a child "child". Use master__child without the parent__ in it to make it more readable.
https://www.smashingmagazine.com/2016/06/battling-bem-extended-edition-common-problems-and-how-to-avoid-them/
- Redefine atom design components

src/routes/credits.svelte

@@ -48,7 +48,7 @@
 
         <div class="page__list">
             {#each credits as category}
-            <div class="page__list--category">
+            <div class="page__category">
                 <h2 class="title-category">{category.name}</h2>
                 {#each category.credits as person}
                 <dl>