Remove double btn-default definition

Increase btn-default border darkness - refs #7539

main/css/chamilo/default.css

@@ -6630,7 +6630,7 @@ button.close {
   filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#ffffffff', endColorstr='#fff5f5f5', GradientType=0);
   -webkit-filter: none;
           filter: none;
-  border-bottom: 1px solid #e6e6e6;
+  border: 1px solid #d5d5d5;
 }
 .btn-default:hover {
   color: #555555;
@@ -6638,17 +6638,6 @@ button.close {
 .btn-default .caret {
   border-top-color: #555555;
 }
-.btn-default {
-  background-image: -webkit-linear-gradient(#ffffff, #ffffff 60%, #f5f5f5);
-  background-image: -o-linear-gradient(#ffffff, #ffffff 60%, #f5f5f5);
-  background-image: -webkit-gradient(linear, left top, left bottom, from(#ffffff), color-stop(60%, #ffffff), to(#f5f5f5));
-  background-image: linear-gradient(#ffffff, #ffffff 60%, #f5f5f5);
-  background-repeat: no-repeat;
-  filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#ffffffff', endColorstr='#fff5f5f5', GradientType=0);
-  -webkit-filter: none;
-          filter: none;
-  border-bottom: 1px solid #e6e6e6;
-}
 .btn-primary {
   background-image: -webkit-linear-gradient(#54b4eb, #2fa4e7 60%, #1d9ce5);
   background-image: -o-linear-gradient(#54b4eb, #2fa4e7 60%, #1d9ce5);