diff --git a/style/debug.css b/style/debug.css
new file mode 100644
index 0000000..3e3ce77
--- /dev/null
+++ b/style/debug.css
@@ -0,0 +1,43 @@
+.partouter {
+    border-style: solid;
+    border-width: 1px;
+    border-color: #0000FF;
+}
+
+.partinner {
+    border-style: dotted;
+    border-width: 1px;
+    border-color: #0000FF;
+}
+
+.partheader {
+    background-color: #0000FF;
+    color: #FFFFFF;
+    font-size: 70%;
+}
+
+th {
+    text-align: left;
+}
+
+.subject {
+    font-size: 1.2em;
+    color: #000088;
+}
+
+.text-enriched {
+    font-family: monospace;
+    white-space: pre-wrap;
+}
+
+.signature {
+    font-size: 0.8rem;
+}
+
+.dubious {
+    background-color: #888800;
+}
+
+.partinner.html {
+    max-width: 40rem;
+}
diff --git a/templates/body_text_html.html b/templates/body_text_html.html
index a42fbb4..f55d620 100644
--- a/templates/body_text_html.html
+++ b/templates/body_text_html.html
@@ -2,7 +2,7 @@
     <div class="partheader">
         text/html
     </div>
-    <div class="partinner">
+    <div class="partinner html">
         {{body}}
     </div>
 </div>