Use the correct class for the landing image

Author: moeenio

index.html

@@ -15,7 +15,7 @@ <h1>Ease your eyes on Scratch</h1>
       <p>Bring back the old Scratch 2 blue to the Scratch website and editor, instead of the new flashy, eye-hurting blue.</p>
       <a class="button primary" href="https://raw.githubusercontent.com/csourcesc/old-scratch-blue/master/old-scratch-blue.user.css">Get the userstyle</a>
       <a class="button" href="https://github.com/csourcesc/old-scratch-blue">GitHub repo</a>
-      <img class="image-block" src="sidebyside.png" alt="Side-by-side comparison: Scratch with and without the usertyle">
+      <img class="main-img" src="sidebyside.png" alt="Side-by-side comparison: Scratch with and without the usertyle">
       <footer>
         <small>A project from</small>
         <br>