Fix domain label position and color (#9033)

* Fix position of the domain label

* Fix position of the domain label for RTL

- Fix color mismatch of linear gradient which assigned to "::after" pseudo class

app/javascript/styles/mastodon/forms.scss

@@ -427,7 +427,7 @@ code {
 
     &__append {
       position: absolute;
-      right: 1px;
+      right: 3px;
       top: 1px;
       padding: 10px;
       padding-bottom: 9px;

app/javascript/styles/mastodon/rtl.scss

@@ -246,12 +246,12 @@ body.rtl {
 
   .simple_form .label_input__append {
     right: auto;
-    left: 0;
+    left: 3px;
 
     &::after {
       right: auto;
       left: 0;
-      background-image: linear-gradient(to left, rgba($ui-base-color, 0), $ui-base-color);
+      background-image: linear-gradient(to left, rgba(darken($ui-base-color, 10%), 0), darken($ui-base-color, 10%));
     }
   }