Remove nonstandard block-axis 1px margins from textarea default styles.

dholbert · moz-wptsync-bot · commit aafdb1daad99 · 2026-03-06T01:43:26.000Z
These 1px margins were added (with no explanation/bug-link) in 1999, here: https://searchfox.org/firefox-main/diff/784c6428b65d9539cc8f5e30d18e59a050740007/layout/html/document/src/html.css#1293 They're not part of the html spec, and Chromium/WebKit don't have them; and at least one web developer has run up against them as a sharp edge (causing a textarea with 'height:100vh' to unexpectedly overflow the viewport). So, let's just remove them. As part of this change, we can also simplify the reference cases for reftest ua-style-sheet-textarea-1.html - it had two reference cases which had two different ways to confirm that we properly interpret these logical block-axis margins. Now that the margins are gone, there's no point in having two different reference cases (they end up ~identical once their margin declarations are removed), so this patch merges the reference cases into a single one with no need to specify margins. Differential Revision: https://phabricator.services.mozilla.com/D286187 bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1875156 gecko-commit: 5545120859d3f38c45a1109125481c8fbe84224d gecko-reviewers: layout-reviewers, firefox-style-system-reviewers, emilio
diff --git a/html/rendering/replaced-elements/the-textarea-element/textarea-defaults-to-zero-margin.tentative.html b/html/rendering/replaced-elements/the-textarea-element/textarea-defaults-to-zero-margin.tentative.html
@@ -0,0 +1,22 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>Test: textarea should default to zero margins</title>
+<link rel="help" href="https://html.spec.whatwg.org/multipage/rendering.html#the-textarea-element-2">
+<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1875156">
+<link rel="author" title="Daniel Holbert" href="mailto:dholbert@mozilla.com">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<body>
+  <textarea id="myTextarea"></textarea>
+  <script>
+test(function() {
+  const marginProps = ["margin-top", "margin-right",
+                       "margin-bottom", "margin-left"];
+
+  const cs = window.getComputedStyle(myTextarea, "");
+  marginProps.forEach((prop)=> {
+    assert_equals(cs[prop], "0px",
+                  `computed value of '${prop}' should default to "0px"`);
+  });
+}, "HTML textarea should default to having 0px as computed value for all margin properties")
+</script>
