fix(button): Fixes an issue where visited a[dt-button] components had…

… the wrong style.

Visited anchor tags that were represented as buttons were not styled correctly in dark mode.
The necessary selectors have been added to mitigate this problem.

Fixes #1202

libs/barista-components/button/src/_button-theme.scss

@@ -55,6 +55,7 @@ a.dt-button-primary:visited {
 
 .dt-theme-dark {
   .dt-button-primary,
+  a.dt-button-primary:visited,
   .dt-button-primary:hover:not([disabled]),
   .dt-button-primary:active:not([disabled]) {
     border-color: #ffffff;
@@ -115,7 +116,8 @@ a.dt-button-secondary:visited {
 
 .dt-theme-dark {
   .dt-button-secondary,
-  .dt-button-secondary[disabled] {
+  .dt-button-secondary[disabled],
+  a.dt-button-secondary:visited {
     background: transparent;
     color: #ffffff;
 
@@ -148,10 +150,12 @@ a.dt-button-secondary:visited {
     }
   }
   .dt-button-secondary,
+  a.dt-button-secondary:visited,
   .dt-button-secondary:hover:not([disabled]) {
     border-color: #ffffff;
     color: $gray-100;
   }
+  a.dt-button-secondary:visited,
   .dt-button-secondary:active:not([disabled]) {
     border-color: #ffffff;
     color: #ffffff;