fix: 优化背景图滑动逻辑，确保居中显示、左右滑动完整，全内容可拖动到预览区

css/style.css

@@ -66,12 +66,24 @@ html, body {
     position: relative;
 }
 
+/* 空提示 - 移到预览白板中 */
 .empty-tip {
+    position: absolute;
+    top: 50%;
+    left: 50%;
+    transform: translate(-50%, -50%);
     color: #999;
     font-size: 14px;
+    text-align: center;
+    pointer-events: none;
+    z-index: 5;
 }
 
 /* 预览区域固定 3:5 比例，打开即显示空白面板 */
+.preview {
+    overflow: hidden;
+}
+
 .image-container {
     display: flex;
     position: relative;
@@ -81,6 +93,9 @@ html, body {
     box-shadow: 0 4px 20px rgba(0,0,0,0.15);
     background: #fff;
     overflow: hidden;
+    touch-action: pan-x;
+    margin: 0 auto;
+    contain: layout style paint;
 }
 
 .image-container.empty {
@@ -88,13 +103,40 @@ html, body {
     border: 2px dashed #ddd;
 }
 
-/* 背景图自适应铺满容器，超出部分裁剪 */
-#bgImage {
-    display: block;
+/* 背景图层 - 用于滑动调整位置，溢出隐藏 */
+.preview-bg-layer {
+    position: absolute;
+    top: 0;
+    left: 0;
     width: 100%;
     height: 100%;
-    object-fit: cover;
-    object-position: center;
+    overflow: hidden;
+}
+
+/* 输入框图层 - 与背景图层隔离 */
+.preview-input-layer {
+    position: absolute;
+    top: 0;
+    left: 0;
+    width: 100%;
+    height: 100%;
+    pointer-events: none;
+}
+
+/* 输入框可交互 */
+.preview-input-layer .text-input {
+    pointer-events: auto;
+}
+
+/* 背景图 - 保持比例，可滑动调整位置 */
+#bgImage {
+    display: block;
+    position: absolute;
+    height: 100%;
+    width: auto;
+    max-width: none;
+    left: 50%;
+    transform: translateX(-50%);
     -webkit-user-drag: none;
 }
 
@@ -102,14 +144,15 @@ html, body {
     display: none;
 }
 
-/* 文字输入框 - 透明无边框设计 */
+/* 文字输入框 - 透明无边框设计，黑色微软雅黑16px */
 .text-input {
     position: absolute;
     min-width: 80px;
     min-height: 32px;
     padding: 4px 8px;
-    font-size: 18px;
-    color: #333;
+    font-size: 16px;
+    color: #000;
+    font-family: "Microsoft YaHei", "微软雅黑", sans-serif;
     background: transparent;
     border: 2px solid transparent;
     border-radius: 4px;
@@ -120,6 +163,11 @@ html, body {
     -webkit-user-select: none;
     user-select: none;
     transition: border-color 0.2s;
+    z-index: 10;
+    /* 确保输入框内容超出时不影响父容器和其他元素 */
+    overflow: visible;
+    max-width: none;
+    box-sizing: border-box;
 }
 
 /* 选中状态（单击/长按） - 仅显示虚线边框 */