[2.0.x] Refs #28457 -- Updated the colors of the 'Congrats' page for WCAG AA compliance.

Backport of f6b5cecc71 from master

django/views/templates/default_urlconf.html

@@ -25,7 +25,7 @@
           a {
             background-color: transparent;
             -webkit-text-decoration-skip: objects;
-            color: #20AA76;
+            color: #19865C;
             text-decoration: none;
           }
           img {
@@ -221,7 +221,7 @@
             line-height: 20px;
             max-width: 390px;
             margin: 15px auto 0;
-            color: gray;
+            color: #747755;
           }
           .next-step {
             max-width: 120px;
@@ -274,14 +274,14 @@
             margin-right: 10px;
           }
           .option h4 {
-            color: #20AA76;
+            color: #19865C;
             font-size: 19px;
           }
           .option p {
             font-weight: 300;
             font-size: 15px;
             padding-top: 3px;
-            color: #8f8f8f;
+            color: #757575;
           }
           @media (max-width: 996px) {
             body, footer {