feature/bug: Enable variable/dynamic width stacked notifications

[aarontcannon]

Setting the following css enables variable/dynamic width notifications when stacked={false}

'.Toastify__toast': {
    padding: 0,
    width: 'fit-content',
},
'.Toastify__toast-body': {
    padding: 0,
    margin: 0,
    width: '100%',
},

When I set stacked={true} this no longer works and the notifications are all set to a fixed small width causing all the notifications to run off the screen. Maybe it makes sensed for stacked notifications to all be the same width (visually), but would be interested in seeing if there are ideas for how it could be accomplished with variable/dynamic width.