diff --git a/LayoutTests/platform/ios-wk2/fast/attachment/cocoa/wide-attachment-rendering-expected.txt b/LayoutTests/platform/ios-wk2/fast/attachment/cocoa/wide-attachment-rendering-expected.txt
index 8304d34d042d..d1854cc1548b 100644
--- a/LayoutTests/platform/ios-wk2/fast/attachment/cocoa/wide-attachment-rendering-expected.txt
+++ b/LayoutTests/platform/ios-wk2/fast/attachment/cocoa/wide-attachment-rendering-expected.txt
@@ -49,7 +49,7 @@ layer at (0,0) size 800x600
             RenderGrid {DIV} at (76,0) size 262x92
               RenderGrid {DIV} at (6,26) size 230x40
                 RenderBlock {DIV} at (190,0) size 40x40
-                  RenderButton {BUTTON} at (0,0) size 40x40 [bgcolor=#EEEEEF]
+                  RenderButton {BUTTON} at (0,0) size 40x40 [bgcolor=#7676801F]
                     RenderBlock (anonymous) at (0,9) size 40x22
                       RenderBlock {DIV} at (9,0) size 22x22
 layer at (128,131) size 230x17
diff --git a/Source/WebCore/css/CSSValueKeywords.in b/Source/WebCore/css/CSSValueKeywords.in
index 2cab52776aeb..413c5449029c 100644
--- a/Source/WebCore/css/CSSValueKeywords.in
+++ b/Source/WebCore/css/CSSValueKeywords.in
@@ -273,6 +273,7 @@ accentcolortext
 -apple-system-label enable-if=WTF_PLATFORM_COCOA
 -apple-system-secondary-label enable-if=WTF_PLATFORM_COCOA
 -apple-system-tertiary-label enable-if=WTF_PLATFORM_COCOA
+-apple-system-tertiary-fill enable-if=WTF_PLATFORM_COCOA
 -apple-system-quaternary-label enable-if=WTF_PLATFORM_COCOA
 -apple-system-grid enable-if=WTF_PLATFORM_COCOA
 -apple-system-separator enable-if=WTF_PLATFORM_COCOA
@@ -305,7 +306,6 @@ accentcolortext
 -apple-system-selected-text-background enable-if=WTF_PLATFORM_MAC
 -apple-system-unemphasized-selected-text-background enable-if=WTF_PLATFORM_MAC
 -apple-system-find-highlight-background enable-if=WTF_PLATFORM_MAC
--apple-system-tertiary-fill enable-if=WTF_PLATFORM_MAC
 -apple-system-indigo enable-if=WTF_PLATFORM_IOS_FAMILY
 -apple-system-teal enable-if=WTF_PLATFORM_IOS_FAMILY
 -apple-system-opaque-fill enable-if=WTF_PLATFORM_IOS_FAMILY
diff --git a/Source/WebCore/css/parser/CSSParserIdioms.cpp b/Source/WebCore/css/parser/CSSParserIdioms.cpp
index 626e76126062..57ab7b7f9c03 100644
--- a/Source/WebCore/css/parser/CSSParserIdioms.cpp
+++ b/Source/WebCore/css/parser/CSSParserIdioms.cpp
@@ -39,7 +39,7 @@ bool isValueAllowedInMode(unsigned short id, CSSParserMode mode)
     switch (id) {
     case CSSValueWebkitFocusRingColor:
         return isUASheetBehavior(mode) || isQuirksModeBehavior(mode);
-#if PLATFORM(MAC)
+#if PLATFORM(COCOA)
     case CSSValueAppleSystemTertiaryFill:
 #endif
 #if PLATFORM(IOS_FAMILY)
diff --git a/Source/WebCore/html/shadow/attachmentElementShadow.css b/Source/WebCore/html/shadow/attachmentElementShadow.css
index 8c9c03356903..efd3a212e954 100644
--- a/Source/WebCore/html/shadow/attachmentElementShadow.css
+++ b/Source/WebCore/html/shadow/attachmentElementShadow.css
@@ -182,7 +182,7 @@ button#attachment-save-button {
 #if (defined(WTF_PLATFORM_IOS_FAMILY) && WTF_PLATFORM_IOS_FAMILY)
     width: 40px;
     height: 40px;
-    background-color: -apple-system-opaque-tertiary-fill;
+    background-color: -apple-system-tertiary-fill;
     border: 0;
 #else
     width: 28px;
diff --git a/Source/WebCore/rendering/RenderThemeIOS.mm b/Source/WebCore/rendering/RenderThemeIOS.mm
index 9304f572da86..64d3498ef26c 100644
--- a/Source/WebCore/rendering/RenderThemeIOS.mm
+++ b/Source/WebCore/rendering/RenderThemeIOS.mm
@@ -1425,6 +1425,7 @@ static bool shouldUseConvexGradient(const Color& backgroundColor)
             // FIXME: <rdar://problem/75538507> UIKit should expose this color so that we maintain parity with system buttons.
             { CSSValueAppleSystemOpaqueSecondaryFillDisabled, @selector(secondarySystemFillColor), true, 0.75f },
             { CSSValueAppleSystemOpaqueTertiaryFill, @selector(tertiarySystemFillColor), true },
+            { CSSValueAppleSystemTertiaryFill, @selector(tertiarySystemFillColor) },
             { CSSValueAppleSystemQuaternaryFill, @selector(quaternarySystemFillColor) },
             { CSSValueAppleSystemGroupedBackground, @selector(systemGroupedBackgroundColor) },
             { CSSValueAppleSystemSecondaryGroupedBackground, @selector(secondarySystemGroupedBackgroundColor) },