Add bootstrap classes (#567)

index.html

@@ -138,7 +138,7 @@ <h1>Welcome to <span class=" org-display-name">Public Lab</span>'s coding commun
 
       <hr />
 
-      <h4 style="text-align:center;font-weight:bold;">We're so happy to meet you! This page is to welcome new contributors. </h4>
+      <h4 class="text-center"><b>We're so happy to meet you! This page is to welcome new contributors.</b></h4>
 
       <hr />
 
@@ -169,11 +169,11 @@ <h4 style="text-align:center;font-weight:bold;">We're so happy to meet you! This
 
       <h2>Learn our process</h2>
 
-      <p style="text-align: center;">We have a welcoming "workflow" that supports you in getting started, then helps you reach out to welcome someone else in turn!</p>
+      <p class="text-center">We have a welcoming "workflow" that supports you in getting started, then helps you reach out to welcome someone else in turn!</p>
 
       <br />
 
-      <div class="row section" style="text-align: center;">
+      <div class="row section"  class="text-center">
 
         <div class="col-md-4">
 
@@ -332,7 +332,7 @@ <h2 class="contributors-head" id="contributer">Contributors</h2>
           <div title="copy to clipboard" class="copybutton"><i class="fa fa-clipboard" aria-hidden="true"></i></div>
         </div>
 
-        <div class="well contributors"><div id="spinner-icon" style="text-align: center;"><i class="fa fa-spinner fa-spin"></i></div><p class="usernames"></p><hr /><p class="avatars text-center"></p></div>
+        <div class="well contributors"><div id="spinner-icon" class="text-center"><i class="fa fa-spinner fa-spin"></i></div><p class="usernames"></p><hr /><p class="avatars text-center"></p></div>
       </div>