fix: fixed styling for modal headers (className fcc-modal) (#35220)

client/src/components/layouts/global.css

@@ -33,3 +33,14 @@ h6 {
 a:hover, a:focus {
    text-decoration: none;
 }
+
+.fcc-modal {
+  background-color: #006400;
+  color: #fff;
+}
+
+.fcc-modal .close {
+  color: #fff;
+  font-size: 28px;
+  text-shadow: none;
+}

client/src/templates/Challenges/components/completion-modal.css

@@ -10,6 +10,15 @@
   width: 30vh;
 }
 
+.night .challenge-list-header {
+  background-color: #333;
+  border-bottom-color: #222;
+}
+
+.night .challenge-success-modal .modal-content {
+  background-color: #333;
+}
+
 @media screen and (max-width: 767px) {
   .challenge-success-modal .btn-lg {
     font-size: 16px;