style(CoursesPage): 调整横幅标题字体大小从3xl改为2xl

@@ -29,7 +29,7 @@
             <div
               class="absolute inset-0 bg-gradient-to-b from-transparent to-black/50 flex flex-col justify-end p-4"
             >
-              <h2 class="text-3xl font-bold text-amber-400 drop-shadow-md">{{ banner.post_title }}</h2>
+              <h2 class="text-2xl font-bold text-amber-400 drop-shadow-md">{{ banner.post_title }}</h2>
               <p class="text-xl text-white font-semibold drop-shadow-sm">{{ banner.post_excerpt }}</p>
             </div>
           </van-swipe-item>