Add CSS environment for three column layout

diff --git a/doc/doxygen/stylesheet.css b/doc/doxygen/stylesheet.css
index cb455ae1c6610b9e3ea3fed5b306de6ee3b9bf67..fb64fdfe9fde94beb0472ab6f1ef9139ca4e1a7b 100644 (file)
--- a/doc/doxygen/stylesheet.css
+++ b/doc/doxygen/stylesheet.css
@@ -46,6 +46,18 @@ div.image img[src="fe_enriched_h-refinement.png"] {
     width:500px;
 }
 
+/*
+ * environment for aligning pictures in three columns.
+ */
+.threecolumn {
+  display: grid;
+  grid-template-columns: 1fr 1fr 1fr;
+  grid-column-gap: 5%;
+  grid-row-gap: 5%;
+  margin-left: auto;
+  margin-right: auto;
+}
+
 /*
  * environment for aligning pictures in two columns.
  */