style: 优化后台设置卡片的边框与阴影样式

src/routes/admin/settings/+page.svelte

@@ -385,13 +385,12 @@
 	}
 
 	.settings-card {
-		border: 1px solid var(--border-color, rgba(0, 0, 0, 0.1));
+		border: 1px solid var(--text-color);
+		box-shadow: 0 4px 20px rgba(0, 0, 0, 0.03);
 		padding: 24px;
-		background: var(--bg-surface, #ffffff);
-		border-radius: 6px;
+		background: var(--bg-color, #ffffff);
 		display: flex;
 		flex-direction: column;
-		box-shadow: 0 2px 8px rgba(0, 0, 0, 0.02);
 	}
 
 	.info-grid {