diff --git a/syntax/css.vim b/syntax/css.vim
index 2bd152d..5cee353 100644
--- a/syntax/css.vim
+++ b/syntax/css.vim
@@ -7,7 +7,7 @@
 "               Nikolai Weibull (Add CSS2 support)
 " URL:          https://github.com/vim-language-dept/css-syntax.vim
 " Maintainer:   Jay Sitter <jay@jaysitter.com>
-" Last Change:  2024 Nov 12
+" Last Change:  2025 Nov 07
 
 " quit when a syntax file was already loaded
 if !exists("main_syntax")
@@ -193,7 +193,14 @@ syn keyword cssBorderAttr contained thin thick medium
 
 " box-decoration-break attributes
 syn keyword cssBorderAttr contained clone slice
+
 "------------------------------------------------
+" CSS Masking Module Level 1
+" https://www.w3.org/TR/css-masking-1/
+syn match cssMaskProp contained "\<mask\(-\(image\|mode\|repeat\|position\|clip\|origin\|size\|composite\|type\)\)\=\>"
+syn keyword cssMaskAttr contained none luminance alpha match-source
+syn keyword cssMaskAttr contained add subtract intersect exclude
+syn keyword cssMaskAttr contained fill-box stroke-box view-box no-clip
 
 syn match cssBoxProp contained "\<padding\(-\(top\|right\|bottom\|left\)\)\=\>"
 syn match cssBoxProp contained "\<margin\(-\(top\|right\|bottom\|left\)\)\=\>"
@@ -657,6 +664,8 @@ hi def link cssProp StorageClass
 hi def link cssAttr Constant
 hi def link cssUnitDecorators Number
 hi def link cssNoise Noise
+hi def link cssMaskProp cssProp
+hi def link cssMaskAttr cssAttr
 
 let b:current_syntax = "css"
 
diff --git a/test.css b/test.css
index 3eeb5d4..f3e4f83 100644
--- a/test.css
+++ b/test.css
@@ -343,3 +343,30 @@ and (max-device-width:1024px)
   background-position-x: 20px;
   background-position-y: 20px;
 }
+
+/* mask properties tests */
+#mask-test {
+  mask: url('{!URLFOR($Resource.images)}/mask.png') no-repeat 50% 50% / contain, linear-gradient(black,transparent);
+  mask: none;
+  mask-image: url('{!URLFOR($Resource.images)}/mask.png'), linear-gradient(black, transparent);
+  mask-image: linear-gradient(black, transparent);
+  mask-mode: none;
+  mask-mode: alpha;
+  mask-mode: match-source;
+  mask-position: top;
+  mask-position: bottom;
+  mask-position: center;
+  mask-size: cover;
+  mask-repeat: repeat-x;
+  mask-origin: content-box;
+  mask-composite: add;
+  mask-composite: subtract;
+  mask-composite: intersect;
+  mask-composite: exclude;
+  mask-type: luminance;
+  mask-clip: padding-box;
+  mask-clip: fill-box;
+  mask-clip: stroke-box;
+  mask-clip: view-box;
+  mask-clip: no-clip;
+}