title: CSS - dynamically calculate width
body: <p>I come across <code>width: calc(25% - 20px + 5px);</code></p>
  
  <p>I couldn't find any answer via google. I wanted to know how to get the width to be 410px for three boxes in each row, because right now it returns me 4 boxes in smaller width than 410px. </p>
  
  <p>Any help or insight will be appreciated.</p>