Project shows: Using 3 calls to document.querySelector(…) and 2 calls to document.querySelector(…).addEventListener(‘click’, function () {…}). The query selectors are linked to the *.html files DOM elements, as are the add event listeners.

<!DOCTYPE html>

<!DOCTYPE html>
<html lang=“en”>
  <head>
    <meta charset=“UTF-8” />
    <meta name=“viewport” content=“width=device-width, initial-scale=1.0” />
    <meta http-equiv=“X-UA-Compatible” content=“ie=edge” />
    <link rel=“stylesheet” href=“style.css” />
    <title>Guess My Number!</title>
  </head>
  <body>
    <header>
      <h1>Guess My Number!</h1>
      <p class=“between”>(Between 1 and 20)</p>
      <button class=“btn again”>Again!</button>
      <div class=“number”>?</div>
    </header>
    <main>
      <section class=“left”>
        <input type=“number” class=“guess” />
        <button class=“btn check”>Check!</button>
      </section>
      <section class=“right”>
        <p class=“message”>Start guessing…</p>
        <p class=“label-score”>💯 Score: <span class=“score”>20</span></p>
        <p class=“label-highscore”>
          🥇 Highscore: <span class=“highscore”>0</span>
        </p>
      </section>
    </main>
    <script src=“script.js”></script>
  </body>
</html>
‘use strict’;

let secretNumber = Math.trunc(Math.random() * 20) + 1;
let score = 20;
let highScore = 0;

const displayMessage = function (message) {
  document.querySelector(‘.message’).textContent = message;
};

const displayScore = function (score) {
  document.querySelector(‘.score’).textContent = score;
};

const displayNumber = function (number) {
  document.querySelector(‘.number’).textContent = number;
};

document.querySelector(‘.check’).addEventListener(‘click’, function () {
  const guess = Number(document.querySelector(‘.guess’).value);
  console.log(guess, typeof guess);

  // When no guess
  if (!guess) {
    displayMessage(‘No Number!’);
    // When player wins
  } else if (guess === secretNumber) {
    displayMessage(‘😊Correct Number!’);
    document.querySelector(‘body’).style.backgroundColor = ‘#60b347’;
    document.querySelector(‘.number’).style.width = ’30rem’;
    displayNumber(secretNumber);
    if (score > highScore) {
      highScore = score;
      document.querySelector(‘.highscore’).textContent = highScore;
    }
    // When guess is wrong
  } else if (guess !== secretNumber) {
    if (score > 1) {
      displayMessage(guess > secretNumber ? ‘↑ To High!’ : ‘↓ Too Low!’);
      score—;
    } else {
      displayMessage(‘😒You lost the game!’);
      score = 0;
    }
    displayScore(score);
  }
});

document.querySelector(‘.again’).addEventListener(‘click’, function () {
  displayMessage(‘Start guessing…’);
  document.querySelector(‘body’).style.backgroundColor = ‘#222’;
  document.querySelector(‘.guess’).value = ”;
  displayNumber(‘?’);
  document.querySelector(‘.number’).style.width = ’15rem’;
  score = 20;
  displayScore(score);
  secretNumber = Math.trunc(Math.random() * 20) + 1;
});
@import url(‘https://fonts.googleapis.com/css?family=Press+Start+2P&display=swap’);

* {
  margin: 0;
  padding: 0;
  box-sizing: inherit;
}

html {
  font-size: 62.5%;
  box-sizing: border-box;
}

body {
  font-family: ‘Press Start 2P’, sans-serif;
  color: #eee;
  background-color: #222;
  /* background-color: #60b347; */
}

/* LAYOUT */
header {
  position: relative;
  height: 35vh;
  border-bottom: 7px solid #eee;
}

main {
  height: 65vh;
  color: #eee;
  display: flex;
  align-items: center;
  justify-content: space-around;
}

.left {
  width: 52rem;
  display: flex;
  flex-direction: column;
  align-items: center;
}

.right {
  width: 52rem;
  font-size: 2rem;
}

/* ELEMENTS STYLE */
h1 {
  font-size: 4rem;
  text-align: center;
  position: absolute;
  width: 100%;
  top: 52%;
  left: 50%;
  transform: translate(-50%, -50%);
}

.number {
  background: #eee;
  color: #333;
  font-size: 6rem;
  width: 15rem;
  padding: 3rem 0rem;
  text-align: center;
  position: absolute;
  bottom: 0;
  left: 50%;
  transform: translate(-50%, 50%);
}

.between {
  font-size: 1.4rem;
  position: absolute;
  top: 2rem;
  right: 2rem;
}

.again {
  position: absolute;
  top: 2rem;
  left: 2rem;
}

.guess {
  background: none;
  border: 4px solid #eee;
  font-family: inherit;
  color: inherit;
  font-size: 5rem;
  padding: 2.5rem;
  width: 25rem;
  text-align: center;
  display: block;
  margin-bottom: 3rem;
}

.btn {
  border: none;
  background-color: #eee;
  color: #222;
  font-size: 2rem;
  font-family: inherit;
  padding: 2rem 3rem;
  cursor: pointer;
}

.btn:hover {
  background-color: #ccc;
}

.message {
  margin-bottom: 8rem;
  height: 3rem;
}

.label-score {
  margin-bottom: 2rem;
}