diff --git a/src/styles/diff.css b/src/styles/diff.css
index 269c315..f81b1a4 100644
--- a/src/styles/diff.css
+++ b/src/styles/diff.css
@@ -1,10 +1,19 @@
 /* Diff layout + line colors. Everything is scoped under `pre.dh-on` so toggling
    the extension off (which removes that class) fully restores the plain view. */
 
+/* Chrome's text/plain body has margin: 8px by default. Zero it out so the pre
+   fills the viewport exactly — no margin overflow, no phantom scrollbar. */
+body:has(pre.dh-on) {
+  margin: 0;
+  padding: 0;
+}
+
 pre.dh-on {
   margin: 0;
   padding: 12px 0;
-  min-height: 100vh;
+  /* overflow-x: auto keeps long lines scrollable within the pre itself rather
+     than spilling to the page and causing a page-level horizontal scrollbar. */
+  overflow-x: auto;
   box-sizing: border-box;
   tab-size: 4;
   font: 12px/1.5 ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas,