diff --git a/css/main.scss b/css/main.scss
index 65491ff..32f1139 100644
--- a/css/main.scss
+++ b/css/main.scss
@@ -150,4 +150,23 @@ code .result-lang
 @media (min-width: 550px) {
   .title { font-size: 7.0rem; } 
   .logo { width: 64px; }
-}
\ No newline at end of file
+}
+
+/* show source and rendition side-by-side */
+@media (min-width: 1000px) {
+  pre.language-html.line-numbers,
+  div.preview.markdown-body {
+    margin: 0.5em 4% 1em 0; /* 4% like .columns */
+    width: 48%; /* like .six.columns */
+    float: left; /* like .columns */    box-sizing: border-box; /* like .columns */
+  }
+  pre.language-html.line-numbers {
+    max-width: 80ch; /* improve legibility */
+  }
+  div.preview.markdown-body {
+    margin-left: 0; /* like .colums:first-child */
+  }
+  .markdown-body::before, .markdown-body::after {
+    display: none;
+  }
+}