fix: center video modal properly on screen

Co-authored-by: Cursor <cursoragent@cursor.com>

components/top-navbar.tsx

@@ -453,14 +453,14 @@ export function TopNavbar({
       {/* 功能教程弹窗 */}
       {showTutorialModal && currentTutorialVideo && (
         <div 
-          className="fixed inset-0 z-[100] flex items-center justify-center bg-black/80"
+          className="fixed inset-0 z-[100] flex items-center justify-center bg-black/90 p-4"
           onClick={() => {
             setShowTutorialModal(false);
             setCurrentTutorialVideo(null);
           }}
         >
           <div 
-            className="relative w-full max-w-4xl mx-4"
+            className="relative w-full max-w-5xl max-h-[90vh] flex flex-col"
             onClick={(e) => e.stopPropagation()}
           >
             {/* 标题和关闭按钮 */}