tailwind css is not working with my templete css

in my templete i used custom css but now some clasess of tailwind css is not working the bellow code only text with out bg and other clasess

   <div class="flex justify-center mt-4">
                    
                    <button type="submit"
                     class="w-full h-12 px-6 text-indigo-100 transition-colors duration-150 
                     bg-indigo-700 rounded-lg focus:shadow-outline
                      hover:bg-indigo-800">Save
                    </button>
                    
                </div>