diff --git a/browser2/js/TODO.MD b/browser2/js/TODO.MD
index 1f9dbbd..318350e 100644
--- a/browser2/js/TODO.MD
+++ b/browser2/js/TODO.MD
@@ -2,3 +2,4 @@
 * create consistency with the `lingo-app` container element. It needs to be passed into `renderLingoApp` and is also referenced in various places in markup.js as the id `lingo-app` or via closest css `.closest('.lingo-container')`.
 * delete `handleSequenceOps` and move logic to custom functions which will be placed in the function lookup
 * add type checking when using `set` to update a struct's value
+* ~~responsive CSS: mobile and desktop support~~ ✅ done (fluid layout, mobile ≤600px / tablet 601–900px breakpoints, table scroll wrappers)
diff --git a/browser2/js/src/markup.js b/browser2/js/src/markup.js
index 1504883..42768a7 100644
--- a/browser2/js/src/markup.js
+++ b/browser2/js/src/markup.js
@@ -3594,7 +3594,10 @@ function createValueElement(app, element, ctx = null) {
         }
         table.appendChild(tbody);
         
-        return table;
+        const wrapper = document.createElement('div');
+        wrapper.className = 'table-scroll-wrapper';
+        wrapper.appendChild(table);
+        return wrapper;
 
     } else if(element.type == 'list') {
         const listFormat = (element.display && element.display.format) ? element.display.format : 'bullets';
@@ -3751,7 +3754,10 @@ function createValueElement(app, element, ctx = null) {
             }
             table.appendChild(tbody);
             
-            return table;
+            const wrapper = document.createElement('div');
+            wrapper.className = 'table-scroll-wrapper';
+            wrapper.appendChild(table);
+            return wrapper;
         }else if(listFormat == 'bullets' || listFormat == 'numbers') {
 
             let elementType;
diff --git a/browser2/js/src/style.css b/browser2/js/src/style.css
index d2daf46..3bc3f63 100644
--- a/browser2/js/src/style.css
+++ b/browser2/js/src/style.css
@@ -1,14 +1,23 @@
 /**
  * Browser 2.0 JavaScript Renderer Styles
+ *
+ * Responsive breakpoints:
+ *   mobile  : max-width 600px
+ *   tablet  : 601px – 900px
+ *   desktop : 901px+  (base styles, max-width 1000px centred)
  */
 
 /* Base styles */
 body {
     font-family: Verdana, sans-serif;
     font-size: 12px;
-    margin: 20px;
+    margin: 0;
+    padding: 16px;
     background-color: white;
+    box-sizing: border-box;
     max-width: 1000px;
+    margin-left: auto;
+    margin-right: auto;
 }
 
 /* Heading styles */
@@ -29,18 +38,21 @@ h6 { font-size: 16px; }
 }
 
 /* Form element styles */
-input[type="text"] {
-    padding: 5px;
-    border: 1px solid #ccc;
-    border-radius: 3px;
-    width: 233px;
+input[type="text"],
+input[type="password"],
+input[type="email"],
+select,
+textarea {
+    width: 100%;
+    max-width: 400px;
+    box-sizing: border-box;
 }
 
+input[type="text"],
 input[type="password"] {
     padding: 5px;
     border: 1px solid #ccc;
     border-radius: 3px;
-    width: 233px;
 }
 
 button {
@@ -182,4 +194,73 @@ table td {
     padding: 20px;
     border-radius: 5px;
     z-index: 100;
+}
+
+/* Navigation / breadcrumb styles */
+.breadcrumb {
+    display: flex;
+    flex-wrap: wrap;
+    gap: 4px;
+}
+
+/* Table scroll wrapper — allows horizontal scrolling on narrow screens */
+.table-scroll-wrapper {
+    overflow-x: auto;
+    -webkit-overflow-scrolling: touch;
+}
+
+/* Mobile breakpoint */
+@media (max-width: 600px) {
+    body {
+        padding: 8px;
+        font-size: 13px;
+    }
+
+    h1 { font-size: 24px; }
+    h2 { font-size: 20px; }
+    h3 { font-size: 18px; }
+    h4 { font-size: 16px; }
+
+    .form-table td {
+        display: block;
+        width: 100%;
+    }
+
+    button {
+        width: 100%;
+        margin: 4px 0;
+    }
+
+    input[type="text"],
+    input[type="password"],
+    input[type="email"],
+    select,
+    textarea {
+        max-width: 100%;
+        width: 100%;
+    }
+
+    .lingo-container {
+        padding: 10px;
+        border-width: 2px;
+    }
+
+    .popup-content {
+        width: 90%;
+        left: 5%;
+        top: 10%;
+    }
+}
+
+/* Tablet breakpoint */
+@media (min-width: 601px) and (max-width: 900px) {
+    body { padding: 12px; }
+
+    input[type="text"],
+    input[type="password"],
+    input[type="email"],
+    select,
+    textarea {
+        max-width: 300px;
+    }
 }
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