diff --git a/src/OEBPS/Text/advanced_topics.xhtml b/src/OEBPS/Text/advanced_topics.xhtml
index 7b409ed..c75502a 100644
--- a/src/OEBPS/Text/advanced_topics.xhtml
+++ b/src/OEBPS/Text/advanced_topics.xhtml
@@ -249,6 +249,11 @@ QFrame QToolButton#count {
 }
 </code></pre>
 
+<p><b>Change the QDockWidget Close and UnDock Icon size.</b> (This will affect Preview, Table of Contents, BookBrowser, Clips, and Validation windows)</p>
+<pre><code>QDockWidget::float-button, QDockWidget::close-button {
+  icon-size: 16px;
+}
+</code></pre>
 
 <p>This is just a smattering of the styling changes you can make to Sigil using Qt's QSS styles.  For further information about QSS and Sigil visit our <a href="https://www.mobileread.com/forums/forumdisplay.php?f=203">Mobileread Sigil Users Forum</a> and check out these website resources about Qt styles:</p>
 <ul>