How remove vertical gap between characters ?

 html

    

<style>
.FlexColumn {display: flex;flex-flow: column nowrap }
</style>

<div class="FlexColumn">
    <div>X</div>
    <div>X</div>
    <div>X</div>
    <div>X</div>
    <div>X</div>
</div>

  

 html

    
<!-- I tried many CSS trick here... -->
<div>
   <span>X</span><br><span>X</span><br><span>X</span><br><span>X</span>
</div>