Minor CSS tweaks (#227)

docs/extra.css

@@ -22,3 +22,12 @@ input {
         height: 48px;
     }
 }
+
+.text-center {
+    text-align: center !important;
+}
+
+/* needed because images have `max-width: 100%` in the theme */
+img {
+    height: auto;
+}

docs/ftldns/index.md

@@ -1,4 +1,8 @@
-<p align="center"><img src="../images/FTLDNS.png" alt="FTLDNS"><br><strong>powered by Pi-hole®</strong></p>
+<p class="text-center">
+    <img src="../images/FTLDNS.png" alt="FTLDNS" width="690" height="184">
+    <br>
+    <strong>powered by Pi-hole®</strong>
+</p>
 
 *FTL*DNS[™](https://pi-hole.net/trademark-rules-and-brand-guidelines/) (`pihole-FTL`) offers DNS services within the Pi-hole[®](https://pi-hole.net/trademark-rules-and-brand-guidelines/) project.
 It provides blazing fast DNS and DHCP services. It can also provide TFTP and more as the resolver part based on the popular `dnsmasq`. Furthermore, FTL offers an interactive API where extensive network analysis data and statistics may be queried.

docs/index.md

@@ -4,7 +4,7 @@ description: Brief overview of Pi-hole
 last_updated: Thur May 02 01:00:00 2019 UTC
 ---
 
-<p style="text-align: center;">
+<p class="text-center">
     <a href="https://pi-hole.net/">
         <img src="https://pi-hole.github.io/graphics/Vortex/Vortex_with_Wordmark.svg" width="150" height="260" alt="Pi-hole">
     </a>