--- a/src/html.cpp Tue Feb 25 17:51:50 2025 +0100
+++ b/src/html.cpp Tue Feb 25 17:56:54 2025 +0100
@@ -72,7 +72,8 @@
puts("<div class=\"heatmap-content\">");
indentation = 1;
} else {
- puts(R"(<html>
+ puts(R"(<!DOCTYPE html>
+<html>
<head>
<style>
table.heatmap {