diff --git a/src/App.tsx b/src/App.tsx
index 984842c..049ca76 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -98,7 +98,7 @@ function App() {
 
   return (
     <div className="min-h-screen bg-gradient-to-br from-slate-50 to-slate-100">
-      <main className="container mx-auto px-4 py-6 max-w-7xl">
+      <main className="container mx-auto px-4 py-6 max-w-[1920px]">
         {/* Header */}
         <div className="mb-6">
           <FileChooser
@@ -113,8 +113,8 @@ function App() {
 
         {envs.length > 0 ? (
           <div className="grid grid-cols-1 lg:grid-cols-12 gap-6">
-            {/* Environment Panel */}
-            <section className="lg:col-span-4 xl:col-span-4">
+            {/* Environment Panel - Fixed 4/12 on all large screens */}
+            <section className="lg:col-span-4 xl:col-span-4 2xl:col-span-3">
               <div className="sticky top-6">
                 <Environment
                   envs={envs}
@@ -126,8 +126,8 @@ function App() {
               </div>
             </section>
 
-            {/* Content Panel */}
-            <section className="lg:col-span-8 xl:col-span-8">
+            {/* Content Panel - Maximum width (8/12 → 9/12 on 2xl) */}
+            <section className="lg:col-span-8 xl:col-span-8 2xl:col-span-9">
               <Content
                 env={currentEnv}
                 config={config}