diff --git a/book/source/_static/epub/css/custom.css b/book/source/_static/epub/css/custom.css
index bd7da7c..e1791ca 100644
--- a/book/source/_static/epub/css/custom.css
+++ b/book/source/_static/epub/css/custom.css
@@ -13,4 +13,41 @@ div.admonition {
 div.warning,
 div.admonition-warning {
   background-color: palevioletred;
+}
+
+/*
+External links
+*/
+a.external.reference {
+  border-bottom: 1px solid darkgreen;
+  color: darkgreen;
+  text-decoration: none;
+}
+
+/*
+Internal links
+*/
+a.internal {
+  text-decoration: none;
+  border-bottom-style: none;
+}
+
+/*
+Text in section and reference links and footnote links
+*/
+span.std-doc,
+span.std-numref,
+span.std-ref,
+a.footnote-reference {
+  border-bottom: 1px dashed #3333ff;
+  color: #3333ff;
+  text-decoration: none;
+}
+
+/*
+Text in glossary links
+*/
+span.std-term {
+  color: black;
+  border-bottom: 1px dotted black;
 }
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