Pnotify center position

Apply below class:

.ui-pnotify{
   left: 50%;
   margin-left: -150px;
}

Note: Margin left should be half of your div width.

Eg: If div width is 300px then margin left will be -150px.

CSS horizontal centering of a fixed div

Apply below class to your div which is position fixed:

.div-position-fixed-centered-align{
   left: 50%;
   margin-left: -150px;
}

Note: Margin left should be half of your div width.

Eg: If div width is 300px then margin left will be -150px.