fix: remove dropdown title, improve video modal centering

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

components/top-navbar.tsx

@@ -276,9 +276,6 @@ export function TopNavbar({
               </Button>
             </DropdownMenuTrigger>
             <DropdownMenuContent align="end" className="w-[320px] p-2">
-              <div className="text-sm font-medium text-muted-foreground mb-2 px-2">
-                选择教程视频
-              </div>
               <div className="space-y-1 max-h-[400px] overflow-y-auto">
                 {tutorialVideos
                   .sort((a, b) => a.order - b.order)
@@ -450,33 +447,34 @@ export function TopNavbar({
         />
       )}
 
-      {/* 功能教程弹窗 */}
+      {/* 功能教程弹窗 - 全屏居中 */}
       {showTutorialModal && currentTutorialVideo && (
         <div 
-          className="fixed inset-0 z-[100] flex items-center justify-center bg-black/90 p-4"
+          className="fixed top-0 left-0 right-0 bottom-0 z-[9999] flex items-center justify-center bg-black/95"
+          style={{ margin: 0, padding: 0 }}
           onClick={() => {
             setShowTutorialModal(false);
             setCurrentTutorialVideo(null);
           }}
         >
           <div 
-            className="relative w-full max-w-5xl max-h-[90vh] flex flex-col"
+            className="relative w-[90vw] max-w-[1200px] mx-auto"
             onClick={(e) => e.stopPropagation()}
           >
-            {/* 标题和关闭按钮 */}
-            <div className="flex items-center justify-between mb-4">
-              <h3 className="text-white text-lg font-medium">{currentTutorialVideo.title}</h3>
-              <button
-                onClick={() => {
-                  setShowTutorialModal(false);
-                  setCurrentTutorialVideo(null);
-                }}
-                className="text-white hover:text-gray-300 transition-colors"
-                title="关闭"
-              >
-                <X className="h-8 w-8" />
-              </button>
-            </div>
+            {/* 关闭按钮 - 右上角 */}
+            <button
+              onClick={() => {
+                setShowTutorialModal(false);
+                setCurrentTutorialVideo(null);
+              }}
+              className="absolute -top-12 right-0 text-white hover:text-gray-300 transition-colors z-10"
+              title="关闭"
+            >
+              <X className="h-10 w-10" />
+            </button>
+            
+            {/* 标题 */}
+            <h3 className="text-white text-xl font-medium mb-4 text-center">{currentTutorialVideo.title}</h3>
             
             {/* 视频播放器 */}
             {currentTutorialVideo.videoUrl.includes('youtube.com') || currentTutorialVideo.videoUrl.includes('youtu.be') ? (