Add linux/windows download buttons

Summary:
There's probably a more elegant way for doing this
so please let me know if you can think of something.

Reviewed By: danielbuechele

Differential Revision: D17318727

fbshipit-source-id: 9afcc30205171cfb07f0a749c552692cb40a3ced

website/pages/en/index.js

@@ -22,9 +22,19 @@ class Index extends React.Component {
             </h2>
             <div className="row">
               <a
-                className="landing-btn primary"
+                className="landing-btn landing-btn-left primary"
                 href="https://www.facebook.com/fbflipper/public/mac">
-                Download
+                Download Mac
+              </a>
+              <a
+                className="landing-btn landing-btn-middle primary"
+                href="https://www.facebook.com/fbflipper/public/linux">
+                Linux
+              </a>
+              <a
+                className="landing-btn landing-btn-right primary"
+                href="https://www.facebook.com/fbflipper/public/windows">
+                Windows
               </a>
               <a className="landing-btn" href="/docs/features/index.html">
                 Learn more

website/static/css/custom.css

@@ -55,18 +55,41 @@ h6 {
 .landing-btn {
   display: inline-block;
   padding: 7px 20px;
-  border-radius: 6px;
   margin: 0 10px;
+  border-radius: 6px;
   border: 1px solid #777;
 }
 
-.landing-btn:hover {
+.landing-btn-left {
+  border-top-right-radius: 0;
+  border-bottom-right-radius: 0;
+  margin-right: 0;
+  padding-right: 10px;
+}
+
+.landing-btn-middle {
+  border-radius: 0;
+  margin: 0;
+  padding: 7px 10px;
+}
+
+.landing-btn-right {
+  border-top-left-radius: 0;
+  border-bottom-left-radius: 0;
+  margin-left: 0;
+  padding-left: 10px;
+}
+
+.landing-btn.primary:hover {
+  background-color: #0066af;
+  border-color: #0066af;
 }
 
 .landing-btn.primary {
   background-color: #008cf2;
   color: white;
   border-color: #008cf2;
+  color: white;
 }
 
 .splash .landing-btn {