Manual: Fix fullscreen mode. (#22953)

* fixes #22890

* revert to width style in .fullscreen class

manual/resources/lesson.css

@@ -232,9 +232,9 @@ div[data-diagram] {
 }
 .fullscreen {
     position: fixed !important;
-    left: 0;
+    left: var(--panel-width);
     top: 0;
-    width: 100% !important;
+    width: calc(100% - var(--panel-width)) !important;
     height: 100% !important;
     z-index: 100;
 }