开始对话界面背景图切换+开始对话框居中

src/App.vue

@@ -579,7 +579,7 @@ async function handleVoiceQueryComplete(text: string) {
   align-items: flex-start;
   justify-content: center;
   padding-top: clamp(70px, 28vh, 300px);
-  /* 科技感深色背景：参考图中数据中心/服务器走廊氛围 */
+  /* 背景图片 + 科技感深色遮罩 */
   background:
     /* 底部中央全息平台高光 */
     radial-gradient(
@@ -614,14 +614,18 @@ async function handleVoiceQueryComplete(text: string) {
     linear-gradient(90deg, rgba(59, 130, 246, 0.12) 0%, transparent 12%),
     linear-gradient(270deg, rgba(59, 130, 246, 0.12) 0%, transparent 12%),
     /* 顶部暗角与底部辉光 */
-    radial-gradient(ellipse at 50% 0%, rgba(7, 10, 18, 0.9) 0%, transparent 45%),
+    radial-gradient(ellipse at 50% 0%, rgba(7, 10, 18, 0.7) 0%, transparent 45%),
     radial-gradient(
       ellipse at 50% 100%,
       rgba(30, 64, 175, 0.25) 0%,
       transparent 50%
     ),
-    /* 基础深色 */
-    linear-gradient(180deg, #05070c 0%, #0a0f1c 40%, #0d1424 100%);
+    /* 深色遮罩叠加在背景图上 */
+    linear-gradient(180deg, rgba(5, 7, 12, 0.75) 0%, rgba(10, 15, 28, 0.55) 50%, rgba(13, 20, 36, 0.75) 100%),
+    url("./assets/background.jpg");
+  background-size: cover;
+  background-position: center;
+  background-repeat: no-repeat;
 
   /* 两侧服务器架网格线纹理 */
   &::before,
@@ -1588,7 +1592,8 @@ async function handleVoiceQueryComplete(text: string) {
 /* 1440×1920 分辨率专用优化 */
 @media (width: 1440px) and (height: 1920px) {
   .connect-overlay {
-    padding-top: 26vh;
+    align-items: center;
+    padding-top: 0;
   }
 
   .connect-card {
@@ -1694,7 +1699,8 @@ async function handleVoiceQueryComplete(text: string) {
 /* 1080×1920 分辨率专用优化 */
 @media (width: 1080px) and (height: 1920px) {
   .connect-overlay {
-    padding-top: 26vh;
+    align-items: center;
+    padding-top: 0;
   }
 
   .connect-card {
@@ -1799,7 +1805,8 @@ async function handleVoiceQueryComplete(text: string) {
 /* 1440×2560 分辨率专用优化 */
 @media (width: 1440px) and (height: 2560px) {
   .connect-overlay {
-    padding-top: 30vh;
+    align-items: center;
+    padding-top: 0;
   }
 
   .connect-card {