Added and used color from varibales file (#457)

amundsen_application/static/css/_variables-default.scss

@@ -18,6 +18,7 @@ $body-bg-tertiary:  $gray5 !default;
 $body-bg-dark:      $gray100 !default;
 $divider:           $gray15 !default;
 $stroke:            $gray20 !default;
+$stroke-light:      $gray10 !default;
 $stroke-focus:      $gray60 !default;
 
 

amundsen_application/static/js/components/TableDetail/TableIssues/styles.scss

@@ -8,9 +8,9 @@
     padding: 8px;
     display: flex;
     flex-direction: row;
-    border-top: 2px solid $gray10;
-    border-bottom: 2px solid $gray10;
-    color: $gray60;
+    border-top: 1px solid $stroke-light;
+    border-bottom: 1px solid $stroke-light;
+    color: $text-secondary;
   }
   .table-issue-link {
     margin-right: $spacer-1;