diff --git a/.travis.yml b/.travis.yml
index 1b3b8ef..6897827 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,14 +1,17 @@
 language: ruby
+
 rvm:
-  - 2.2.2
+  - 2.6.3
+
+env:
+  global:
+    - NOKOGIRI_USE_SYSTEM_LIBRARIES=true # speeds up installation of html-proofer
+
 addons:
   apt:
     packages:
     - libcurl4-openssl-dev # required to avoid SSL errors
-sudo: false
+
 script:
   - bundle exec jekyll build
   - bundle exec htmlproofer '_site/' --allow-hash-href --check-html --http-status-ignore 0
-env:
-  global:
-    - NOKOGIRI_USE_SYSTEM_LIBRARIES=true # speeds up installation of html-proofer
diff --git a/404.html b/404.html
index 3646366..90c6fe6 100644
--- a/404.html
+++ b/404.html
@@ -14,7 +14,7 @@ permalink: 404.html
           <div class="has-text-centered">
             <img
               src="{{ '/media/unknown_node.jpg' | relative_url }}"
-              alt=""
+              alt="Unknown node"
             >
 
             <h2>Sorry, we could not find that page!</h2>
diff --git a/_config.yml b/_config.yml
index 9e9c075..5327be6 100644
--- a/_config.yml
+++ b/_config.yml
@@ -4,6 +4,8 @@ plugins:
 sass:
   style: compressed
 exclude:
+  # `vendor/` is excluded because of <https://github.com/jekyll/jekyll/issues/3330>
+  - vendor/
   - CNAME
   - Gemfile
   - LICENSE.md
diff --git a/_includes/footer.html b/_includes/footer.html
index bd8dd2e..e3c4909 100644
--- a/_includes/footer.html
+++ b/_includes/footer.html
@@ -3,7 +3,7 @@
     <div class="columns is-multiline">
 
       <div class="column is-6 is-3-desktop">
-        <h3 class="footer-title">Minetest</h5>
+        <h5 class="footer-title">Minetest</h5>
         <ul class="list-unstyled">
           <li><a href="/#features">Features</a></li>
           <li><a href="/#gallery">Gallery</a></li>
@@ -14,7 +14,7 @@
       </div>
 
       <div class="column is-6 is-3-desktop">
-        <h3 class="footer-title">Content</h5>
+        <h5 class="footer-title">Content</h5>
         <ul class="list-unstyled">
           <li><a href="https://content.minetest.net">ContentDB</a></li>
           <li><a href="/customize/#featured">Featured</a></li>
@@ -28,7 +28,7 @@
         <h5 class="footer-title">Community</h5>
         <ul class="list-unstyled">
           <li><a href="https://forum.minetest.net">Forums</a></li>
-          <li><a href="/get_involved/#internet-relay-chat">IRC</a></li>
+          <li><a href="/get-involved/#internet-relay-chat">IRC</a></li>
           <li><a href="/servers/">Servers</a></li>
           <li><a href="https://wiki.minetest.net">Player Wiki</a></li>
           <li><a href="https://reddit.com/r/minetest/">Subreddit</a></li>
@@ -39,10 +39,10 @@
         <h5 class="footer-title">Development</h5>
         <ul class="list-unstyled">
           <li><a href="https://github.com/minetest/minetest">Github</a></li>
-          <li><a href="/get_involved/#internet-relay-chat">#minetest-dev on Freenode IRC</a></li>
+          <li><a href="/get-involved/#internet-relay-chat">#minetest-dev on Freenode IRC</a></li>
           <li><a href="https://dev.minetest.net">Developer Wiki</a></li>
           <li><a href="https://minetest.net/lua_api/">Lua API</a></li>
-          <li><a href="/get_involved/#donate">Donate</a></li>
+          <li><a href="/get-involved/#donate">Donate</a></li>
         </ul>
       </div>
 
diff --git a/_includes/header.html b/_includes/header.html
index f7cc880..236b523 100644
--- a/_includes/header.html
+++ b/_includes/header.html
@@ -26,6 +26,7 @@
         <a class="navbar-item" href="{{ '/downloads/' | relative_url }}">Download</a>
         <a class="navbar-item" href="{{ '/customize/' | relative_url }}">Customize</a>
         <a class="navbar-item" href="{{ '/get-involved/' | relative_url }}">Get Involved</a>
+      </div>
     </div>
   </div>
 </nav>
diff --git a/credits.html b/credits.html
index d68089c..488a934 100644
--- a/credits.html
+++ b/credits.html
@@ -93,10 +93,13 @@ redirect_from:
 
         <p class="has-text-weight-bold">
           More information can be found at
-          <a href="https://www.openhub.net/p/minetest-c55">Open Hub</a>.
+          {% comment %}
+            OpenHub seems to be flaky, so ignore it in HTMLProofer link checking.
+          {% endcomment %}
+          <a href="https://www.openhub.net/p/minetest-c55" data-proofer-ignore>Open Hub</a>.
         </p>
         <p>
-          Want to <a href="{{ '/get_involved/#contribute' | relative_url }}">contribute</a>?
+          Want to <a href="{{ '/get-involved/#contribute' | relative_url }}">contribute</a>?
         </p>
 
       </div>
diff --git a/customize.html b/customize.html
index da90a13..a264398 100644
--- a/customize.html
+++ b/customize.html
@@ -14,7 +14,7 @@ redirect_from:
     <div class="content">
 
       <h1>Customize</h1>
-      <h2 class="is-size-3">Content Database</h1>
+      <h2 class="is-size-3">Content Database</h2>
       <p>
         Browse through a ton of content on the ContentDB website.<br>
         You can also install content right from your Minetest client!
@@ -23,9 +23,9 @@ redirect_from:
         <a class="button is-primary" href="https://content.minetest.net">Go to ContentDB</a>
       </p>
 
-      <h2 id="featured">Featured</h1>
+      <h2 id="featured">Featured</h2>
 
-      <h3 id="games">Games</h2>
+      <h3 id="games">Games</h3>
       <p>
         The Minetest Engine runs games.
         Different <a href="http://wiki.minetest.net/Games">games</a> have different objectives –
@@ -47,7 +47,7 @@ redirect_from:
 
       <hr>
 
-      <h3 id="mods">Mods</h2>
+      <h3 id="mods">Mods</h3>
       <p>
         Minetest is meant to be modded. Mods can add or change functionality and content.
         Learn how to <a href="http://dev.minetest.net/Installing_Mods">install and use mods</a>.
@@ -55,7 +55,7 @@ redirect_from:
 
       <div class="columns is-multiline">
         <div class="column is-6 is-4-desktop">
-          <h4>Building</h3>
+          <h4>Building</h4>
           <ul>
             <li><a href="https://forum.minetest.net/viewtopic.php?t=2041">Home Decor</a></li>
             <li><a href="https://forum.minetest.net/viewtopic.php?t=12534">X-Decor</a></li>
@@ -67,7 +67,7 @@ redirect_from:
           </ul>
         </div>
         <div class="column is-6 is-4-desktop">
-          <h4>Map generation</h3>
+          <h4>Map generation</h4>
           <ul>
             <li><a href="https://forum.minetest.net/viewtopic.php?t=14638">Ethereal NG</a></li>
             <li><a href="https://forum.minetest.net/viewtopic.php?t=11271">Indestructible Bedrock Layer</a></li>
@@ -79,7 +79,7 @@ redirect_from:
           </ul>
         </div>
         <div class="column is-6 is-4-desktop">
-          <h4>Player effects</h3>
+          <h4>Player effects</h4>
           <ul>
             <li><a href="https://forum.minetest.net/viewtopic.php?t=4654">3D Armor</a></li>
             <li><a href="https://forum.minetest.net/viewtopic.php?t=4870">Achievements</a></li>
@@ -91,7 +91,7 @@ redirect_from:
           </ul>
         </div>
         <div class="column is-6 is-4-desktop">
-          <h4>Plants, Animals &amp; Monsters</h3>
+          <h4>Plants, Animals &amp; Monsters</h4>
           <ul>
             <li><a href="https://forum.minetest.net/viewtopic.php?t=9019">Farming Redo</a></li>
             <li><a href="https://forum.minetest.net/viewtopic.php?t=629">Animals Modpack</a></li>
@@ -100,7 +100,7 @@ redirect_from:
           </ul>
         </div>
         <div class="column is-6 is-4-desktop">
-          <h4>Environment</h3>
+          <h4>Environment</h4>
           <ul>
             <li><a href="https://forum.minetest.net/viewtopic.php?t=2807">Immersive Sounds</a></li>
             <li><a href="https://forum.minetest.net/viewtopic.php?t=6854">Snow Drift - Snow, Rain, Clouds</a></li>
@@ -109,7 +109,7 @@ redirect_from:
           </ul>
         </div>
         <div class="column is-6 is-4-desktop">
-          <h4>Transport</h3>
+          <h4>Transport</h4>
           <ul>
             <li><a href="https://forum.minetest.net/viewtopic.php?t=4877">Travelnet teleporters</a></li>
             <li><a href="https://forum.minetest.net/viewtopic.php?t=14726">Advanced Trains</a></li>
@@ -118,7 +118,7 @@ redirect_from:
           </ul>
         </div>
         <div class="column is-6 is-4-desktop">
-          <h4>Inventory</h3>
+          <h4>Inventory</h4>
           <ul>
             <li><a href="https://forum.minetest.net/viewtopic.php?t=14088">Crafting Guide</a></li>
             <li><a href="https://forum.minetest.net/viewtopic.php?t=3933">Unified Inventory</a></li>
@@ -127,7 +127,7 @@ redirect_from:
           </ul>
         </div>
         <div class="column is-6 is-4-desktop">
-          <h4>Tools</h3>
+          <h4>Tools</h4>
           <ul>
             <li><a href="https://forum.minetest.net/viewtopic.php?t=628">Mesecons</a></li>
             <li><a href="https://forum.minetest.net/viewtopic.php?t=2155">Pipeworks</a></li>
@@ -136,7 +136,7 @@ redirect_from:
           </ul>
         </div>
         <div class="column is-6 is-4-desktop">
-          <h4>Maintenance</h3>
+          <h4>Maintenance</h4>
           <ul>
             <li><a href="https://forum.minetest.net/viewtopic.php?t=7239">Advanced Area Protection</a></li>
             <li><a href="https://forum.minetest.net/viewtopic.php?t=9376">Protector Redo</a></li>
@@ -151,7 +151,7 @@ redirect_from:
 
       <hr>
 
-      <h3 id="texture-packs">Texture packs</h2>
+      <h3 id="texture-packs">Texture packs</h3>
       <div class="columns is-multiline">
         <div class="column is-6 is-4-desktop">
           <ul>
diff --git a/index.html b/index.html
index 7c38d0f..abe671c 100644
--- a/index.html
+++ b/index.html
@@ -46,7 +46,7 @@ redirect_from:
 
         {% for feature in category.features %}
         <h4 class="title feature-title">{{ feature.title }}</h4>
-        <p>{{ feature.description | markdownify }}</p>
+        {{ feature.description | markdownify }}
         {% endfor %}
       </div>
       {% endfor %}
diff --git a/servers.html b/servers.html
index 3b0be6c..8c09245 100644
--- a/servers.html
+++ b/servers.html
@@ -88,6 +88,7 @@ server_description = A server that I made.
 server_url = &lt;URL to server homepage or forum topic&gt;
 </pre>
         </div>
+      </div>
     </div>
   </div>
 </section>