Add CSS for contents navigator

build/tufte.css

@@ -478,3 +478,50 @@ label.margin-toggle:not(.sidenote-number) {
     width: 100%;
   }
 }
+
+/* contents navigator */
+
+details#chapters {
+  position: fixed;
+  right: 2px;
+  top: 2px;
+  z-index: 300;
+  max-height: 80%;
+  overflow: auto;
+  background-color: #151515;
+  color: #fffff8;
+  text-align: center;
+  border: 3px solid #fffff8;
+  border-radius: 2px;
+}
+
+details#chapters summary {
+  cursor: pointer;
+  display: block;
+  padding: 2px 5px 5px;
+}
+
+details#chapters summary::marker {
+  list-style: none;
+}
+
+details#chapters summary::after {
+  content: "❮❮";
+}
+
+details#chapters[open] summary::after {
+  content: "❯❯";
+}
+
+details#chapters ul {
+  padding: 3px;
+}
+
+details#chapters li {
+  list-style: none;
+  margin: 5px 10px;
+}
+
+details#chapters a {
+  text-shadow: none;
+}