Set a fixed height for sphinx gallery images

... so that lazy loading does not change heights. Without a fixed
height lazy loading of images interferes with anchor links: Clicking a
link goes to a certain position, but then the loaded images add content
and move the anchor to a different position.

Author: timhoffm

doc/_static/mpl.css

@@ -85,6 +85,15 @@ html[data-theme="dark"] .sphx-glr-thumbcontainer {
     background-color: rgb(63, 63, 63);
 }
 
+/* Set a fixed height so that lazy loading does not change heights. Without a fixed
+ * height lazy loading of images interferes with anchor links: Clicking a link goes to
+ * a certain position, but then the loaded images add content and move the anchor to a
+ * different position.
+ */
+.sphx-glr-thumbcontainer img {
+    height: 112px;
+}
+
 /* hide download buttons in example headers
  * https://sphinx-gallery.github.io/stable/advanced.html#hide-the-download-buttons-in-the-example-headers
  */