try this

.readthedocs.yaml

@@ -30,5 +30,4 @@ python:
     - method: pip
       path: .
       extra_requirements:
-        - docs
-  system_packages: true
+        - docs

docs/_templates/indexcontent.html

@@ -7,15 +7,15 @@
     <p><strong>Overview and Hands-on:</strong></p>
     <table class="contentstable">
         <tr>
-            <td width="65%">
+            <td width="60%">
                 <p class="biglink"><a class="biglink" href="{{ pathto("intro") }}">What is BASIN-3D?</a><br/>
                     <span class="linkdescr">Introduction to BASIN-3D</span></p>
                 <p class="biglink"><a class="biglink" href="{{ pathto("concepts") }}">Concepts in BASIN-3D</a><br/>
                     <span class="linkdescr">Short summary of the basic concepts</span></p>
                 <p class="biglink"><a class="biglink" href="{{ pathto("getting_started") }}#">Installation</a><br/>
                     <span class="linkdescr">Instructions on installing BASIN-3D</span></p>
             </td>
-            <td width="75%">
+            <td width="70%">
                 <p class="biglink"><a class="biglink" href="{{ pathto("quick_guide") }}">Quick Guide</a><br/>
                     <span class="linkdescr">Quick guide to basic functions</span></p>
                 <p class="biglink"><a class="biglink" href="{{ pathto("examples") }}">Examples</a><br/>