Fix github message theme border colors, fix tabular segment spacing

src/definitions/collections/menu.less

@@ -681,7 +681,7 @@
   z-index: 2;
 }
 .ui.tabular.menu ~ .bottom.attached.segment {
-  margin: -1px 0px 0px 1px;
+  margin: 0px 0px 0px 1px;
 }
 
 /* Coupling with accordion */

src/themes/packages/github/collections/message.overrides

@@ -1,17 +1,11 @@
 .ui.info.message {
-  background-image: linear-gradient(#D8EBF8, #D0E3EF);
-  border: 1px solid #97C1DA;
-  box-shadow: none;
+  background: linear-gradient(#D8EBF8, #D0E3EF);
 }
 .ui.error.message {
-  background-image: linear-gradient(#F8D8D8, #EFD0D0);
-  border: 1px solid #DA9797;
-  box-shadow: none;
+  background: linear-gradient(#F8D8D8, #EFD0D0);
 }
 .ui.warning.message {
-  background-image: linear-gradient(#FFE3C8, #F5DAC0);
-  border: 1px solid #DCA874;
-  box-shadow: none;
+  background: linear-gradient(#FFE3C8, #F5DAC0);
 }
 .ui.success.message {
 }

src/themes/packages/github/collections/message.variables

@@ -18,6 +18,10 @@
   0px 0px 0px 1px rgba(0, 0, 0, 0.05) inset
 ;
 
+@infoBorderColor: #97C1DA;
+@errorBorderColor: #DA9797;
+@warningBorderColor: #DCA874;
+
 @small: 12px;
 @medium: 13px;
 @large: 14px;