What can I use to substitute    in HTML?

Margin and/or Padding. (css properties), like so:

<p style='padding-left : 10px'>Hello</p>

(It's worth noting that it's generally considered bad-practice to put an inline style like that; you typically declare a selector in an external css file and set the class/whatever appropriately.)

In CSS try:

white-space:nowrap;

I had this problem when I realised I will have empty tags. I didn't want to set a fixed height and it was to late to change the html. I wanted to add a space in the css, the substitute for &nbsp, so I added the space before the element, using :before (it needs to be specified via unicode).

p:before {
    content: "\00a0";
}

Hope this solution helps someone. The solution with padding didn't work for my problem.