<h2>Example 1</h2>
<button onClick="flip()">Flip It</button>
  <div class="flipper">
    <div class="item">1</div>
    <div class="item">2</div>
    <div class="item">3</div>
    <div class="item">4</div>
    <div class="item">5</div>
    <div class="item">6</div>
    <div class="item">7</div>
    <div class="item">8</div>
    <div class="item">9</div>
    <div class="item">10</div>
  </div>

<h2>Example 2</h2>
<div class="tracks">
    <div class="track">
      <h2>The Future (Ft. The R.O.C.)</h2>
      <button>⭐</button>
      <button>❤️</button>
      <button>❌</button>
    </div>
    <div class="track">
      <h2>Bounce With Me (Ft. Jermaine Dupri & Xscape)</h2>
      <button>⭐</button>
      <button>❤️</button>
      <button>❌</button>
    </div>
    <div class="track">
      <h2>Puppy Love (Ft. Jagged Edge & Jermaine Dupri)</h2>
      <button>⭐</button>
      <button>❤️</button>
      <button>❌</button>
    </div>
    <div class="track">
      <h2>You Know Me (Ft. Da Brat & Jermaine Dupri)</h2>
      <button>⭐</button>
      <button>❤️</button>
      <button>❌</button>
    </div>
    <div class="track">
      <h2>The Dog in Me</h2>
      <button>⭐</button>
      <button>❤️</button>
      <button>❌</button>
    </div>
    <div class="track">
      <h2>Bow Wow (That's My Name) (Ft. Snoop Dogg)</h2>
      <button>⭐</button>
      <button>❤️</button>
      <button>❌</button>
    </div>
  </div>

<h2>Example 3</h2>
<div class="controls">
    <button>⏯️</button>
    <button>🐢</button>
    <button>🐰</button>
    <div class="scrubber"></div>
    <button>💬</button>
    <button>🔽</button>
  </div>

<h2>Example 4</h2>
<div class="hero">
  <h2>Something Big Is Coming</h2>
  <p>Get Ready...</p>
</div>

<h2>Example 5</h2>
<div class="corners">
  <div class="corner item">1</div>
  <div class="corner item">TWO</div>
  <div class="corner item">3</div>
  <div class="corner item">4</div>
</div>

<h2>Example 6</h2>
<div class="stacked">
  <div class="item">1</div>
  <div class="item">2</div>
  <div class="item">3</div>
  <div class="item">4</div>
  <div class="item">5</div>
</div>
  
<h2>Example 7</h2>
 <div class="container known">
    <div class="item">Short</div>
    <div class="item">Longerrrrrr</div>
    <div class="item">
      <img src="https://source.unsplash.com/300x200" alt="">
    </div>
    <div class="item">💩</div>
  </div>

<h2>Example 8</h2>
<button onClick="addItem()">+ Add</button>
<div class="unknown">
  <div class="item">1</div>
  <div class="item">2</div>
  <div class="item">3</div>
</div>

<h2>Example 9</h2>
<div class="flex-container">
  <div class="item">Short</div>
  <div class="item">Longerrrrrrrrrrrrrr</div>
  <div class="item">💩</div>
  <div class="item">This is Many Words</div>
  <div class="item">Lorem, ipsum.</div>
  <div class="item">10</div>
  <div class="item">Snickers</div>
  <div class="item">Wes Is Cool</div>
  <div class="item">Short</div>
</div>
:root {
  --yellow: #ffc600;
}

.flipper {
  display: grid;
  grid-gap: 20px;
  grid-template-columns: repeat(auto-fit, minmax(50px, 1fr));
}

.flipper.flip {
  grid-template-columns: 1fr;
}

.item {
  display: grid;
  justify-content: center;
  align-items: center;
  border: 5px solid rgba(0, 0, 0, 0.03);
  border-radius: 3px;
  font-size: 35px;
  background-color: var(--yellow);
}

.item p {
  margin: 0 0 5px 0;
}

.track {
  background: white;
  padding: 10px;
  border-bottom: 1px solid rgba(0, 0, 0, 0.1);
  display: grid;
  grid-template-columns: 1fr;
  grid-auto-flow: column;
}


.controls {
  margin: 200px 0;
  /* display: flex; */
  /* align-items: center; */
  display: grid;
  grid-template-columns: auto auto auto 1fr auto auto;
}

.scrubber {
  background: #BADA55;
  height: 10px;
  min-width: 100px;
  border-radius: 10px;
  /* flex: 1; */
}

.hero {
  height: 200px;
  background: rgba(255, 255, 255, 0.2);
  border: 2px solid red;
  display: grid;
  justify-items: center;
  align-content: center;
  /* display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center; */
}

.corners {
  display: grid;
  height: 200px;
  width: 200px;
  border: 10px solid var(--yellow);
  grid-template: 1fr 1fr / 1fr 1fr;
  align-items: end;
  justify-items: end;
}


.corner:nth-child(1),
.corner:nth-child(2) {
  align-self: start;
}

.corner:nth-child(1),
.corner:nth-child(3) {
  justify-self: start;
}

.stacked {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-around;
  margin-top: 20px;
}

.stacked>* {
  width: 30%;
  margin-bottom: 20px;
}

.known {
  display: grid;
  margin: 20px 0;
  grid-template-columns: repeat(4, 1fr);
  justify-content: center;
  grid-gap: 20px;
}

.unknown {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(50px, 1fr));
  grid-gap: 20px;
}

.flex-container {
  display: flex;
  flex-wrap:wrap;
}

.flex-container>* {
  flex: 1;
  margin: 10px;
}
function flip(e) {
  const flipper =     document.querySelector('.flipper');
  flipper.classList.toggle('flip');
}

function addItem() {
  const unknown = document.querySelector('.unknown');
  unknown.innerHTML += `<div class="item">${unknown.childElementCount}</div>`;
}

External CSS

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External JavaScript

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