diff --git a/css/leptonChrome.css b/css/leptonChrome.css
index 7c6a9b9..43a215f 100644
--- a/css/leptonChrome.css
+++ b/css/leptonChrome.css
@@ -528,6 +528,24 @@
         --win-accent-active-color: -moz-accent-color;
       }
     }
+    @supports -moz-bool-pref("userChrome.compatibility.os.win11") {
+      :root:not(:-moz-lwtheme) {
+        --win-text-color: #1a1a1a;
+        --win-bgcolor: #e8e8e8;
+        --win-hover-bgcolor: #eaeaea; /* also button-bgcolor */
+        --win-disabled-color: #9f9f9f;
+        --win-hover-active-bgcolor: #d9d9d9; /* also button-active-color */
+        --win-button-hover-bgcolor: #d9d9d9;
+        --win-button-active-bgcolor: rgba(46, 46, 46, 0.66);
+        --win-component-bgcolor: #f8f8f8;
+        --win-border-color: #e9e9e9;
+        --win-tab-separator-color: #dadada;
+        --win-sidebar-bgcolor: #ffffff;
+        --win-button-border: var(--win-border-color);
+        --win11-chrome-separator-color: #d6d6d6;
+        --win11-tab-border-color: #dadada;
+      }
+    }
     @media (-moz-toolbar-prefers-color-scheme: dark), (prefers-color-scheme: dark) {
       :root:not(:-moz-lwtheme),
       :root[lwt-default-theme-in-dark-mode] {
@@ -565,6 +583,25 @@
           --win-accent-active-color: -moz-accent-color;
         }
       }
+      @supports -moz-bool-pref("userChrome.compatibility.os.win11") {
+        :root:not(:-moz-lwtheme),
+        :root[lwt-default-theme-in-dark-mode] {
+          --win-bgcolor: #202020;
+          --win-hover-bgcolor: #383838; /* also button-bgcolor */
+          --win-disabled-color: #797979;
+          --win-hover-active-bgcolor: #454545; /* also button-active-color */
+          --win-button-hover-bgcolor: #454545;
+          --win-button-active-bgcolor: rgba(46, 46, 46, 0.66);
+          --win-field-bgcolor: #232323;
+          --win-component-bgcolor: #2c2c2c;
+          --win-border-color: #3d3d3d;
+          --win-tab-separator-color: #323232;
+          --win-sidebar-bgcolor: var(--win-component-bgcolor);
+          --win-button-border: var(--win-border-color);
+          --win11-chrome-separator-color: #3a3a3a;
+          --win11-tab-border-color: #1d1d1d;
+        }
+      }
     }
     :root:not(:-moz-lwtheme),
     :root[lwt-default-theme-in-dark-mode] {
@@ -689,6 +726,15 @@
         }
       }
     }
+    @supports -moz-bool-pref("userChrome.compatibility.os.win11") {
+      :root:not(:-moz-lwtheme),
+      :root[lwt-default-theme-in-dark-mode] {
+        --chrome-content-separator-color: var(--win11-chrome-separator-color) !important;
+      }
+      #nav-bar {
+        --lwt-tabs-border-color: var(--win11-tab-border-color) !important;
+      }
+    }
     /*- Proton Tab Selected ----------------------------------------------------*/
     @supports not -moz-bool-pref("userChrome.tab.color_like_toolbar") {
       :root:not(:-moz-lwtheme),
diff --git a/src/theme/system_default_theme/_win10.scss b/src/theme/system_default_theme/_win10.scss
index 1bd608e..8c92eda 100644
--- a/src/theme/system_default_theme/_win10.scss
+++ b/src/theme/system_default_theme/_win10.scss
@@ -28,6 +28,23 @@
       --win-accent-hover-color: color-mix(in srgb, rgba(255, 255, 255, 0.8) 27%, #{$accentColor});
       --win-accent-active-color: #{$accentColor};
     }
+    @include Option("userChrome.compatibility.os.win11") {
+      --win-text-color: #1A1A1A;
+      --win-bgcolor: #E8E8E8;
+      --win-hover-bgcolor: #EAEAEA; /* also button-bgcolor */ // or #EFEFEF
+      --win-disabled-color: #9F9F9F;
+      --win-hover-active-bgcolor: #D9D9D9; /* also button-active-color */
+      --win-button-hover-bgcolor: #D9D9D9;
+      --win-button-active-bgcolor: rgba(46, 46, 46, 0.66);
+      --win-component-bgcolor: #F8F8F8;
+      --win-border-color: #E9E9E9;
+      --win-tab-separator-color: #DADADA;
+      --win-sidebar-bgcolor: #FFFFFF;
+      --win-button-border: var(--win-border-color);
+
+      --win11-chrome-separator-color: #D6D6D6;
+      --win11-tab-border-color: #DADADA;
+    }
   }
   @include Dark {
     #{system-default-theme()} {
@@ -57,6 +74,24 @@
         --win-accent-hover-color: color-mix(in srgb, rgba(0, 0, 0, 0.8) 5%, #{$accentColor});
         --win-accent-active-color: #{$accentColor};
       }
+
+      @include Option("userChrome.compatibility.os.win11") {
+        --win-bgcolor: #202020;
+        --win-hover-bgcolor: #383838; /* also button-bgcolor */
+        --win-disabled-color: #797979;
+        --win-hover-active-bgcolor: #454545; /* also button-active-color */
+        --win-button-hover-bgcolor: #454545;
+        --win-button-active-bgcolor: rgba(46, 46, 46, 0.66);
+        --win-field-bgcolor: #232323;
+        --win-component-bgcolor: #2C2C2C;
+        --win-border-color: #3D3D3D;
+        --win-tab-separator-color: #323232;
+        --win-sidebar-bgcolor: var(--win-component-bgcolor);
+        --win-button-border: var(--win-border-color);
+
+        --win11-chrome-separator-color: #3A3A3A;
+        --win11-tab-border-color: #1D1D1D;
+      }
     }
   }
 
@@ -209,6 +244,15 @@
     }
   }
 
+  @include Option("userChrome.compatibility.os.win11") {
+    #{system-default-theme()} {
+      --chrome-content-separator-color: var(--win11-chrome-separator-color) !important;
+    }
+    #nav-bar {
+      --lwt-tabs-border-color: var(--win11-tab-border-color) !important;
+    }
+  }
+
   /*- Proton Tab Selected ----------------------------------------------------*/
   @include NotOption("userChrome.tab.color_like_toolbar") {
     #{system-default-theme()} {