title: bootstrap 4 - When to use reboot css and grid css?
body: <p>I am trying to migrate my application from bootstrap 3.3.7 to Bootstrap v4.0.0-alpha.6.</p>
  
  <p>When I downloaded the Bootstrap v4.0.0-alpha.6 into my project using NuGet, I saw bootstrap-reboot.css and bootstrap-grid.css in addition to bootstrap.css.</p>
  
  <p><a href="https://i.stack.imgur.com/yTEe2.png" rel="noreferrer"><img src="https://i.stack.imgur.com/yTEe2.png" alt="enter image description here"></a></p>
  
  <p>I tried to go through the document and understand their purpose but, I am not getting a clear picture.</p>
  
  <p>What is the use of those two css files? Do I really need to include them in my project?</p>