feat(post) : fix margin

src/app/post/components/post-details/post-details.component.html

-<div *ngIf="post">
-  <h2>{{ post.title }}</h2>
+<div *ngIf="post" fxLayout="column">
+  <div fxLayout="row" (click)="backToPosts()">
+    <span>Retour à la liste d'acutalités</span>
+  </div>
 </div>
-
-<button (click)="backToPosts()">Retour</button>

src/app/post/components/post-list/post-list.component.html

-<div class="section-container" fxLayout="row" fxLayoutGap="32px">
+<div fxLayout="row" fxLayoutGap="32px">
   <div fxLayout="column" class="list-container">
     <div fxLayout="column">
       <div fxLayout="row" class="row-border" fxLayoutAlign="space-between center">

src/app/post/post.component.html

 <app-post-header></app-post-header>
-<router-outlet></router-outlet>
+<div class="section-container">
+  <router-outlet></router-outlet>
+</div>