title: How to set empty span height equal to default line height?
body: <p>I have a set of <code>&lt;span&gt;</code> elements (each of them is nested to correspondent <code>&lt;div&gt;</code>). They build a stack of panels, like in the picture below.</p>
  
  <p><img src="https://i.stack.imgur.com/edZBq.png" alt="enter image description here"></p>
  
  <p>When span contains some text, it has a normal height. But when it is empty, it's height is 0px. But I need it to have a normal height (to make it look like in the picture).</p>
  
  <p>How to achive this behavior? (I tried to insert a space, but maybe there's a better solution).</p>