What is the HTML equivalent for   (space) in Dash?
html.Div(
[
dcc.Input(),
<add horizontal space here>
dcc.Input()
]
)
If you want to add some space between components you can simply use CSS-properties for this:
html.Div(
[
dcc.Input(),
dcc.Input(style={"margin-left": "15px"})
]
)
This adds a margin to the left of your second Input.
Have a look at the layout-section in the Plotly Dash documentation and CSS documentation about margin: