Oops! That page can’t be found.

Go to admin > Settings->Permalinks
set first options: defualt (https://localhost/project/wordpress/?p=123) then click on Save changes and check in front if its working fine then again set

Post name : https://localhost/project/wordpress/sample-post/

and let me know its working or not

thanks you so much it is working.

can you please help me to change my sidebar colour.

Yes sure, which color you need to put ?

.sidebar .widget {background-color : red;}