I think this is what you mean to achieve:
#PersonalToolbar#PersonalToolbar{
background: none !important;
}
#PlacesToolbar{
justify-content: center;
}
#PlacesToolbarItems{
max-width: min-content;
background-color: var(--toolbar-bgcolor);
}
Except for "blur" - with which I think you mean blurring of whatever is behind the bar - but that isn't possible in this scenario. If the bar was to appear over the toolbar area then you could blur the toolbar content behind the box.