Use one container and semantic sections for index page

templates/frontpage/blocks/claim.html

-<div class="container">
-    <section class="columns is-centered is-half">
+<section class="section">
+    <div class="columns is-centered is-half">
         <h1 class="title is-1">Eine verstehbare, digitale Welt</h1>
-    </section>
-    <section class="columns">
+    </div>
+    <div class="columns">
         <div class="column"><div class="box is-shadowless"><h1 class="title is-3">Technik hinterfragen</h1><p>TBA</p></div></div>
         <div class="column"><div class="box is-shadowless"><h1 class="title is-3">Digitale Mündigkeit</h1><p>TBA</p></div></div>
         <div class="column"><div class="box is-shadowless"><h1 class="title is-3">Mitgestalten statt konsumieren</h1><p>TBA</p></div></div>
-    </section>
-</div>
+    </div>
+</section>
\ No newline at end of file

templates/frontpage/blocks/news.html

-<div class="container">
-  <section class="columns is-centered is-half">
+<section class="section">
+  <div class="columns is-centered is-half">
     <h1 class="title is-1">Neuigkeiten</h1>
-  </section>
-  <section class="columns is-same-height">
+  </div>
+  <div class="columns is-same-height">
     <div class="column">
       <div class="card is-shadowless">
         <div class="card-image">
@@ -85,6 +85,5 @@
         </div>
       </div>
     </div>
-  </section>
-  <br />
-</div>
\ No newline at end of file
+  </div>
+</section>

templates/frontpage/blocks/projects.html

-<div class="container">
-  <section class="columns is-centered is-half">
+<section class="section">
+  <div class="columns is-centered is-half">
     <h1 class="title is-1">Unsere Projekte</h1>
-  </section>
-  <section class="columns">
+  </div>
+  <div class="columns">
     <div class="column">
       <div class="card">
         <figure class="image is-4by3">
@@ -74,6 +74,5 @@
         </div>
       </div>
     </div>
-  </section>
-  <br />
-</div>
+  </div>
+</section>

templates/index.html

 {% extends "base.html" %}
 
 {% block main %}
-  {% include "frontpage/blocks/claim.html" %}
-  {% include "frontpage/blocks/news.html" %}
-  {% include "frontpage/blocks/projects.html" %}
-  {% include "frontpage/blocks/events.html" %}
+  <div class="container">
+    {% include "frontpage/blocks/claim.html" %}
+    {% include "frontpage/blocks/news.html" %}
+    {% include "frontpage/blocks/projects.html" %}
+    {% include "frontpage/blocks/events.html" %}
+  </div>
 {% endblock %}