Puzzle

 ACROSS

  1 Hydrogen, for one

  4 Lab assistant not in Shelley's novel

  8 Sasha or Malia

 13 Eight: Prefix

 15 Tesla, for the Model S, 3, X or Y

 16 "Dunkirk" director Christopher

 17 Reclined

 18 Do a CPA's job

 19 Horn sounds

 20 Good grasps of business? (John Grisham)

 23 New Haven university

 24 "___ we there yet?"

 25 Anonymous love letter senders (Rhonda Byrne)

 32 Admit responsibility

 33 "Stretch" ride

 34 Average guy

 35 Satisfactory

 36 Intoxicating

 38 Tableland

 39 Tallahassee sch.

 40 Hum, as an engine

 41 Be silent, in music

 42 Flashes of glory (Stephen King)

 46 "... man ___ mouse?"

 47 Arrow groove

 48 Netflix horror show (Albert Camus)

 55 One may start with @

 56 Kazakh/Uzbek sea

 57 Bright sign type

 58 Analyze

 59 Ponderous volume

 60 Plus-one at a party

 61 What an angry cat does

 62 Award for Chloe Kim or Roger Federer

 63 Article that can be added to 20-, 25-, 42- and 48-Across' starts to form book titles

DOWN

  1 Part of LPGA

  2 Berry in a bowl

  3 Move to action

  4 Skewer

  5 Birthstone for many Capricorns

  6 Gave the nod to

  7 Single squats, say

  8 Province by four Great Lakes

  9 2020 hopeful Cory

 10 Popular succulent

 11 Welcome sights?

 12 Response to a ques.

 14 "When I give the signal"

 21 Instrument with pedals

 22 Thigh muscle, slangily

 25 Nothing-but-net sound

 26 World-weariness

 27 Wake-up call alternative

 28 Completed

 29 Button in James Bond's car

 30 Flowers in a bouquet

 31 Show to a table

 32 Switch settings

 36 Szechuan cuisine relative

 37 Bit of work

 38 Neil Armstrong made one giant leap for it

 40 They say "Arrr!"

 41 Stanford specialty, for short

 43 What the weary get, it's said

 44 Place to merge

 45 ___ Crue

 48 Trade (with)

 49 Hatcher of "Desperate Housewives"

 50 Golden ___ Bridge

 51 Cupid, to the Greeks

 52 Tidy

 53 Dark makeup wearer, often

 54 Old dagger (SEEN anagram)

 55 Plays a Charmin prank on, briefly

Solution