Another Straightforward 4-letters Crossword?

_{This is an entry for Fortnightly Topic Challenge #43: Variety Crossword Grids.}

Across
4. "___ and on"
5. "La ___" light
6. Aside from it
8. Diagonal
10. Firefly
12. Clothes shop
14. Supersede
16. -ism or -y
18. Area in Da Nang
21. "___ many times do…"
22. Dad and son
23. From readers

Down
1. Strange word
2. "Diana" son
3. Analyze
5. (lit.) Fish
7. Ideal closed
9. "I Agree" (Sumo)
11. Rope’s end
13. "These are ___ times"
15. "Perry Mason"?
17. Should be
19. Aid of a sort
20. An angry act

The final answer will be a 4-words phrase.