How to fill gaps at bottom of airing cupboard?

[adamt11]

Hello,
I have gaps at the bottom of my airing cupboard along the sides, what would be the best way of filling these?
The cupboard smells of smoke that comes from the flat downstairs. I was wondering if expanding foam would do the trick.
Thanks

 

[foxhole]

Possibly , or cut a piece of hardboard to fit the floor exactly.