diff --git a/changelog.txt b/changelog.txt
index 403a0f4..d3ff5b3 100644
--- a/changelog.txt
+++ b/changelog.txt
@@ -1,4 +1,5 @@
 = 1.2.21 =
+* Fixed the back-to-top arrow sitting off-centre in its button. The 36px button's content box was 22px tall and 10px wide after border and padding, so a 18px glyph with a 27px line box could not centre on either axis; measured 2.8px right and 1.9px high before, sub-pixel after
 * Fixed one-page section links in the menu, and the page-builder customizer, using site_url() where home_url() was meant. On installs with WordPress in its own subdirectory those pointed at /wp/ instead of the site address
 * Added add_theme_support( 'wp-block-styles' ) and add_editor_style(), so core block styles apply on the front end and the editor canvas matches the theme's typography
 * Added three block styles (two button styles and a short rule) and two block patterns, built from the theme's own button and colour values
diff --git a/readme.txt b/readme.txt
index 2d791da..cbd2f02 100644
--- a/readme.txt
+++ b/readme.txt
@@ -68,6 +68,7 @@ This page template is used to create the Parallax homepage from our demo : https
 == Changelog ==
 
 = 1.2.21 =
+* Fixed the back-to-top arrow sitting off-centre in its button. The 36px button's content box was 22px tall and 10px wide after border and padding, so a 18px glyph with a 27px line box could not centre on either axis; measured 2.8px right and 1.9px high before, sub-pixel after
 * Fixed one-page section links in the menu, and the page-builder customizer, using site_url() where home_url() was meant. On installs with WordPress in its own subdirectory those pointed at /wp/ instead of the site address
 * Added add_theme_support( 'wp-block-styles' ) and add_editor_style(), so core block styles apply on the front end and the editor canvas matches the theme's typography
 * Added three block styles (two button styles and a short rule) and two block patterns, built from the theme's own button and colour values
diff --git a/style.css b/style.css
index 42f8f8e..b1a7011 100644
--- a/style.css
+++ b/style.css
@@ -3563,7 +3563,22 @@ footer.bg-dark a {
   -webkit-transform: translateX(-50%);
   height: 36px;
   width: 36px;
-  padding: 5px 11px;
+  /*
+   * Centred with flex rather than padding + line-height. The button is a fixed
+   * 36px box, so with a 2px border and 5px/11px padding the content box was
+   * 22px tall and 10px wide -- while the glyph is 18px with a 27px line box
+   * inherited from .btn-sm. Neither axis could centre: the arrow sat 1px high
+   * and 3.4px right of centre, measured on the rendered button.
+   *
+   * letter-spacing is reset because .btn adds 1px after every character,
+   * including the last, which offsets any centred single glyph by half that.
+   */
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  padding: 0;
+  line-height: 1;
+  letter-spacing: 0;
 }
 
 .back-to-top .fa {