Add Dark Mode Support

docs/css/main.css

@@ -1,10 +1,3 @@
-mark {
-    background-color: #ff0;
-    border-radius: 5px;
-    padding-top: 0;
-    padding-bottom: 0;
-}
-
 .indented {
     padding-left: 20px;
 }

docs/njk/common.njk

@@ -1,10 +1,10 @@
 {% macro previous_next(previous_page, next_page) %}
 <div class="clearfix">
 {% if previous_page != ''%}
-<span class="float-start"><a class="btn btn-light" href="{{ previous_page }}.html"><md>:far-arrow-alt-circle-left: <include src="{{ previous_page }}.md#title" inline /></md></a></span>
+<span class="float-start"><a class="btn" href="{{ previous_page }}.html"><md>:far-arrow-alt-circle-left: <include src="{{ previous_page }}.md#title" inline /></md></a></span>
 {% endif %}
 {% if next_page != ''%}
-<span class="float-end"><a class="btn btn-light" href="{{ next_page }}.html"><md><include src="{{ next_page }}.md#title" inline /> :far-arrow-alt-circle-right:</md></a></span>
+<span class="float-end"><a class="btn" href="{{ next_page }}.html"><md><include src="{{ next_page }}.md#title" inline /> :far-arrow-alt-circle-right:</md></a></span>
 {% endif %}
 </div>
 <br>