fix: standardize button background color and add styles for delete completed tasks button

Author: sofragiualina

Sprint-3/todo-list/style.css

@@ -41,7 +41,7 @@ h1 {
 .todo-input button {
   padding: 10px 20px;
   font-size: 16px;
-  background-color: #4CAF50;
+  background-color: #4caf50;
   color: white;
   border: none;
   border-radius: 6px;
@@ -52,6 +52,22 @@ h1 {
   background-color: #45a049;
 }
 
+/* Delete completed tasks button */
+#delete-completed-btn {
+  padding: 10px 20px;
+  font-size: 16px;
+  background-color: #4caf50;
+  color: white;
+  border: none;
+  border-radius: 6px;
+  cursor: pointer;
+  margin-bottom: 20px;
+}
+
+#delete-completed-btn:hover {
+  background-color: #45a049;
+}
+
 .todo-list {
   list-style-type: none;
   padding-left: 0;