diff --git a/chrome.manifest b/chrome.manifest
index f3b05aad0d..9049d5fdfa 100644
--- a/chrome.manifest
+++ b/chrome.manifest
@@ -6,6 +6,11 @@ content	zotero-platform		chrome/content/zotero-platform/unix/      os=SunOS
 content	zotero-platform		chrome/content/zotero-platform/unix/      os=FreeBSD
 content	zotero-platform		chrome/content/zotero-platform/unix/      os=OpenBSD
 
+content	zotero-platform-version chrome/content/zotero-platform/default-version/
+# Big Sur shows up as 10.0
+content	zotero-platform-version chrome/content/zotero-platform/mac-big-sur/ os=Darwin osversion=10.0
+#content	zotero-platform-version chrome/content/zotero-platform/mac-big-sur/ os=Darwin
+
 resource zotero				resource/
 
 # Keep in sync with locale.js and zotero-standalone-build:assets/multilocale.txt
diff --git a/chrome/content/scaffold/scaffold.xul b/chrome/content/scaffold/scaffold.xul
index 6daf6a19c3..79ff544ebb 100644
--- a/chrome/content/scaffold/scaffold.xul
+++ b/chrome/content/scaffold/scaffold.xul
@@ -26,6 +26,7 @@
 <?xml-stylesheet href="chrome://global/skin/" type="text/css"?>
 <?xml-stylesheet href="chrome://scaffold/skin/scaffold.css" type="text/css"?>
 <?xml-stylesheet href="chrome://zotero-platform/content/overlay.css" type="text/css"?>
+<?xml-stylesheet href="chrome://zotero-platform-version/content/style.css"?>
 
 <!DOCTYPE window SYSTEM "chrome://scaffold/locale/scaffold.dtd">
 
diff --git a/chrome/content/zotero-platform/default-version/style.css b/chrome/content/zotero-platform/default-version/style.css
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/chrome/content/zotero-platform/mac-big-sur/style.css b/chrome/content/zotero-platform/mac-big-sur/style.css
new file mode 100644
index 0000000000..077a99cec4
--- /dev/null
+++ b/chrome/content/zotero-platform/mac-big-sur/style.css
@@ -0,0 +1,12 @@
+/* Use standard tab appearance for item pane tabs */
+#zotero-pane #zotero-view-tabbox > tabs > tab {
+	-moz-appearance: tab;
+}
+
+/* Active tab label color in item pane and elsewhere */
+#zotero-pane tabs#zotero-editpane-tabs > tab[visuallyselected="true"][selected="true"] hbox > .tab-text,
+#zotero-prefs tab[visuallyselected="true"]:not(:-moz-window-inactive),
+tabs > tab[visuallyselected="true"] hbox > .tab-text {
+	color: black !important;
+	text-shadow: none;
+}
diff --git a/chrome/content/zotero/longTagFixer.xul b/chrome/content/zotero/longTagFixer.xul
index 408dfc8a2e..2954190c4b 100644
--- a/chrome/content/zotero/longTagFixer.xul
+++ b/chrome/content/zotero/longTagFixer.xul
@@ -1,6 +1,8 @@
 <?xml version="1.0"?>
 <?xml-stylesheet href="chrome://global/skin/" type="text/css"?>
 <?xml-stylesheet href="chrome://zotero/skin/longTagFixer.css" type="text/css"?>
+<?xml-stylesheet href="chrome://zotero-platform-version/content/style.css"?>
+
 <!DOCTYPE window SYSTEM "chrome://zotero/locale/zotero.dtd">
 
 <dialog id="zotero-long-tag-fixer" xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
diff --git a/chrome/content/zotero/preferences/preferences.xul b/chrome/content/zotero/preferences/preferences.xul
index bebd0977aa..28e18b151a 100644
--- a/chrome/content/zotero/preferences/preferences.xul
+++ b/chrome/content/zotero/preferences/preferences.xul
@@ -31,6 +31,7 @@
 <?xml-stylesheet href="chrome://zotero/skin/preferences.css"?>
 <?xml-stylesheet href="chrome://zotero/skin/zotero.css"?>
 <?xml-stylesheet href="chrome://zotero-platform/content/overlay.css"?>
+<?xml-stylesheet href="chrome://zotero-platform-version/content/style.css"?>
 
 <!--
 	To add an observer for a preference change, add an appropriate case in
diff --git a/chrome/content/zotero/zoteroPane.xul b/chrome/content/zotero/zoteroPane.xul
index 606bfdccb7..661dc59396 100644
--- a/chrome/content/zotero/zoteroPane.xul
+++ b/chrome/content/zotero/zoteroPane.xul
@@ -27,6 +27,7 @@
 
 <?xml-stylesheet href="chrome://zotero/skin/overlay.css" type="text/css"?>
 <?xml-stylesheet href="chrome://zotero-platform/content/overlay.css" type="text/css"?>
+<?xml-stylesheet href="chrome://zotero-platform-version/content/style.css"?>
 <?xul-overlay href="chrome://zotero/content/containers/containers.xul"?>
 
 <!DOCTYPE overlay [