update doc style

Author: MaxenceGollier

docs/build/assets/style.css

@@ -0,0 +1,20 @@
+.mi, .mo, .mn {
+  color: #317293;
+}
+
+a {
+  color: #3091d1;
+}
+
+a:visited {
+  color: #3091d1;
+}
+
+a:hover {
+  color: #ff5722;
+}
+
+nav.toc .logo {
+  max-width: 256px;
+  max-height: 256px;
+}