fix: QQ弹窗加hover桥接区域 + 回到顶部按钮透明底

- popup 加 ::before 透明桥接区域(16px)，鼠标可以移到弹窗上
- 回到顶部按钮去掉深色背景，SVG 放大到 42px，默认半透明

css/float-widget.css

@@ -68,6 +68,16 @@
   white-space: nowrap;
 }
 
+/* 透明桥接区域：从 popup 右侧延伸到按钮，防止鼠标移向弹窗时中断 hover */
+.fw-popup::before {
+  content: '';
+  position: absolute;
+  top: 0;
+  right: -16px;
+  width: 16px;
+  height: 100%;
+}
+
 /* 小三角 */
 .fw-popup::after {
   content: '';
@@ -207,6 +217,11 @@
   opacity: 0;
   visibility: hidden;
   transition: all 0.25s ease;
+  background: transparent !important;
+  border: none !important;
+  backdrop-filter: none !important;
+  -webkit-backdrop-filter: none !important;
+  box-shadow: none !important;
 }
 
 .fw-back-top.show {
@@ -215,8 +230,13 @@
 }
 
 .fw-back-top svg {
-  width: 28px;
-  height: 28px;
+  width: 42px;
+  height: 42px;
+  opacity: 0.5;
+  transition: opacity 0.2s ease;
+}
+
+.fw-back-top:hover svg {
   opacity: 0.9;
 }