fix expand and tabs shortcodes to work with strict Content-Security-Policy

When the Content-Security-Policy header has "style-src 'self';"
inine style elements like style="display: none" are not honored
by browsers, so add CSS to the markup classes and style them
display: none

assets/_shortcodes.scss

@@ -31,6 +31,10 @@
     padding: $padding-16;
   }
 
+  .book-expand-expander {
+    display: none;
+  }
+
   input[type="checkbox"]:checked + .book-expand-content {
     display: block;
   }
@@ -56,6 +60,10 @@
     cursor: pointer;
   }
 
+  .book-tabs-radio {
+    display: none;
+  }
+
   .book-tabs-content {
     order: 999; //Move content blocks to the end
     width: 100%;

layouts/shortcodes/expand.html

@@ -4,7 +4,7 @@
       <span>{{ default "Expand" (.Get 0) }}</span>
       <span>{{ default "↕" (.Get 1) }}</span>
     </div>
-    <input type="checkbox" style="display: none" />
+    <input type="checkbox" class="book-expand-expander" />
     <div class="book-expand-content markdown-inner">
       {{ .Inner | markdownify }}
     </div>

layouts/shortcodes/tabs.html

@@ -4,7 +4,7 @@
 
 <div class="book-tabs">
 {{ range $index, $tab :=  .Scratch.Get $group }}
-  <input type="radio" name="{{ $group }}" style="display: none;" id="{{ printf "%s-%d" $group $index }}" {{ if not $index }}checked="checked"{{ end }} />
+  <input type="radio" class="book-tabs-radio" name="{{ $group }}" id="{{ printf "%s-%d" $group $index }}" {{ if not $index }}checked="checked"{{ end }} />
   <label for="{{ printf "%s-%d" $group $index }}">
     {{ $tab.Name }}
   </label>