The problem is that slider has styles without markers considered, so slider with markers needs additional space below, about 1em
is right to fit it, 1.5em
to have some room below. Luckily slider with markers has separate class name and you can simply add CSS like:
.rc-slider-with-marks {
margin-bottom: 1.5em;
}
Or as inline style use:
dcc.Slider(..., style={'marginBottom': '1.5em'})