[FIX] point_of_sale: center align Notification for all screens

Before this commit, the toast Notification would apprear
center aligned only for some screen sizes. In this commit
we adjust it so that is displays properly for any screen
size.

task-2669747

Part-of: odoo/odoo#81226

addons/point_of_sale/static/src/css/pos.css

@@ -3572,8 +3572,7 @@ td {
  */
 
  .pos .notification {
-    min-width: 250px;
-    max-width: 500px;
+    width: 350px;
     background-color: #333333AA;
     color: #fff;
     text-align: center;
@@ -3581,7 +3580,7 @@ td {
     padding: 16px;
     position: fixed;
     z-index: 1;
-    left: 50%;
+    left: calc((100% - 350px - 32px)/2);
     bottom: 5%;
     font-size: 17px;
 }