Add button for github

Author: olgabrani

CHANGELOG.md

@@ -9,7 +9,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 
 - Module discopower: Add style rules and logos for the buttons of the IdPs:
-    - Bitbucket
+  - Bitbucket
+  - Github
 
 
 ## [v2.2.1](https://github.com/rciam/simplesamlphp-module-themevanilla/compare/v2.2.0...v2.2.1) - 2019-07-03

www/resources/images/github-mark.png

@@ -42,3 +42,4 @@ $wechat: #2dc101;
 $qq: #4292FF;
 $epos: #10482A;
 $bitbucket: #0747a6;
+$github: #24292e;

www/resources/images/github.png

@@ -158,5 +158,19 @@
             margin-right: 0;
         }
     }
-
+    &.github {
+        border-color: $github;
+        background: $white url("../images/github.png") no-repeat center center;
+        background-size: 55%;
+        span {
+            display: none;
+        }
+        img {
+            visibility: hidden;
+        }
+        &:hover {
+            background: $white url("../images/github-mark.png") no-repeat center center;
+            background-size: 26px;
+        }
+    }
 }