diff --git a/themes/478d35d8-bc71-41ab-846e-cfa0feef49f6/chrome.css b/themes/478d35d8-bc71-41ab-846e-cfa0feef49f6/chrome.css
new file mode 100644
index 000000000..be5e19d53
--- /dev/null
+++ b/themes/478d35d8-bc71-41ab-846e-cfa0feef49f6/chrome.css
@@ -0,0 +1,35 @@
+
+:root {
+  --letterbox-multiply-calculated: calc(6px * var(--letterbox-multiply-factor));
+}
+
+:root[zen-single-toolbar='true']:not([customizing]) {
+  #zen-appcontent-navbar-container {
+    @media (-moz-bool-pref: 'zen.view.hide-window-controls') {
+      &:not([zen-has-hover='true']):not([has-popup-menu]):not(:focus-within):not(:has(*:is([panelopen='true'], [open='true']))) {
+        height: 0px !important;
+      }
+    }
+  }
+}
+
+:root:not([inDOMFullscreen='true']):not([chromehidden~='location']):not([chromehidden~='toolbar']) {
+  & #zen-tabbox-wrapper {
+    margin-bottom: var(--letterbox-multiply-calculated) !important;
+  }
+  
+  &[zen-single-toolbar='true'] {
+    & #zen-tabbox-wrapper {
+      margin-top: var(--letterbox-multiply-calculated) !important;
+      transition: margin-top 0.15s ease;
+      transition-delay: 0.2s;
+    }
+    & #zen-appcontent-navbar-container[zen-has-hover="true"] + #zen-tabbox-wrapper {
+      margin-top: 0 !important;
+    }
+  }
+  
+  &:not([zen-right-side="true"]) #zen-tabbox-wrapper {
+    margin-right: var(--letterbox-multiply-calculated) !important;
+  }
+}
diff --git a/themes/478d35d8-bc71-41ab-846e-cfa0feef49f6/image.png b/themes/478d35d8-bc71-41ab-846e-cfa0feef49f6/image.png
new file mode 100644
index 000000000..48f36d70c
Binary files /dev/null and b/themes/478d35d8-bc71-41ab-846e-cfa0feef49f6/image.png differ
diff --git a/themes/478d35d8-bc71-41ab-846e-cfa0feef49f6/preferences.json b/themes/478d35d8-bc71-41ab-846e-cfa0feef49f6/preferences.json
new file mode 100644
index 000000000..0d99d7bf4
--- /dev/null
+++ b/themes/478d35d8-bc71-41ab-846e-cfa0feef49f6/preferences.json
@@ -0,0 +1,9 @@
+[
+    {
+        "property": "letterbox.multiply-factor",
+        "label": "Multiply Factor (number)",
+        "type": "string",
+        "defaultValue": "3",
+        "placeholder": "0.5, 1, 2, ..."
+    }
+]
\ No newline at end of file
diff --git a/themes/478d35d8-bc71-41ab-846e-cfa0feef49f6/readme.md b/themes/478d35d8-bc71-41ab-846e-cfa0feef49f6/readme.md
new file mode 100644
index 000000000..d44f93bb8
--- /dev/null
+++ b/themes/478d35d8-bc71-41ab-846e-cfa0feef49f6/readme.md
@@ -0,0 +1,3 @@
+
+# Zen Letterbox
+A simple way to change the width of the letterbox.
diff --git a/themes/478d35d8-bc71-41ab-846e-cfa0feef49f6/theme.json b/themes/478d35d8-bc71-41ab-846e-cfa0feef49f6/theme.json
new file mode 100644
index 000000000..670099792
--- /dev/null
+++ b/themes/478d35d8-bc71-41ab-846e-cfa0feef49f6/theme.json
@@ -0,0 +1,15 @@
+{
+    "id": "478d35d8-bc71-41ab-846e-cfa0feef49f6",
+    "name": "Zen Letterbox",
+    "description": "A simple way to change the width of the letterbox.",
+    "homepage": "",
+    "style": "https://raw.githubusercontent.com/zen-browser/theme-store/main/themes/478d35d8-bc71-41ab-846e-cfa0feef49f6/chrome.css",
+    "readme": "https://raw.githubusercontent.com/zen-browser/theme-store/main/themes/478d35d8-bc71-41ab-846e-cfa0feef49f6/readme.md",
+    "image": "https://raw.githubusercontent.com/zen-browser/theme-store/main/themes/478d35d8-bc71-41ab-846e-cfa0feef49f6/image.png",
+    "author": "p-sw",
+    "version": "1.0.0",
+    "tags": [],
+    "createdAt": "2025-03-03",
+    "updatedAt": "2025-03-03",
+    "preferences": "https://raw.githubusercontent.com/zen-browser/theme-store/main/themes/478d35d8-bc71-41ab-846e-cfa0feef49f6/preferences.json"
+}
\ No newline at end of file