UI: Make change urls compatible with dark theme

Screenshots: https://imgur.com/a/bud9ghg

Change-Id: I76cffe14f56492cf50e9cb1044b5fb616031b7f6

gr-task-plugin/gr-task-plugin-tasks_html.js

diff --git a/gr-task-plugin/gr-task-plugin-tasks_html.js b/gr-task-plugin/gr-task-plugin-tasks_html.js
index 510c534..dd5755b 100644
--- a/gr-task-plugin/gr-task-plugin-tasks_html.js
+++ b/gr-task-plugin/gr-task-plugin-tasks_html.js
@@ -27,6 +27,11 @@
         .red {
           color: #FFA62F;
         }
+        .links {
+          color: var(--link-color);
+          cursor: pointer;
+          text-decoration: underline;
+        }
       </style>
       <template is="dom-if" if="[[task.icon.id]]">
         <gr-tooltip-content