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JavaScript

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HTML 

              
                 <div class="container">
        <div class="card active"
            style="background-image: url('https://images.unsplash.com/photo-1522069169874-c58ec4b76be5?ixlib=rb-1.2.1&ixid=MnwxMjA3fDB8MHxwaG90by1wYWdlfHx8fGVufDB8fHx8&auto=format&fit=crop&w=412&q=80')">
            <h3>GoldFish</h3>
        </div>
        <div class="card"
            style="background-image:url('https://images.unsplash.com/photo-1547382442-d17c21625a44?ixlib=rb-1.2.1&ixid=MnwxMjA3fDB8MHxwaG90by1wYWdlfHx8fGVufDB8fHx8&auto=format&fit=crop&w=387&q=80')">
            <h3>Dolphen</h3>
        </div>
        <div class="card"
            style="background-image: url('https://media.istockphoto.com/photos/underwater-world-with-corals-and-tropical-fish-picture-id472563478?k=20&m=472563478&s=612x612&w=0&h=nc6rQKFct_FC4WFuC9OLJ-I3jJ9QDDWcwNzK4-ar3lU=')">
            <h3>Sea Animals</h3>
        </div>
        <div class="card"
            style="background-image: url('https://images.unsplash.com/photo-1568660357733-823cbddb0f6a?ixlib=rb-1.2.1&ixid=MnwxMjA3fDB8MHxwaG90by1wYWdlfHx8fGVufDB8fHx8&auto=format&fit=crop&w=387&q=80')">
            <h3>Sea Turtle</h3>
        </div>
        <div class="card"
            style="background-image: url('https://images.unsplash.com/photo-1535591273668-578e31182c4f?ixlib=rb-1.2.1&ixid=MnwxMjA3fDB8MHxwaG90by1wYWdlfHx8fGVufDB8fHx8&auto=format&fit=crop&w=870&q=80')">
            <h3>Nemo</h3>
        </div>
    </div>
!

CSS 

              
                * {
  box-sizing: border-box;
}

body {
  margin: 0;
  padding: 0;
  display: flex; /*讓內容在viewport的中間*/
  justify-content: center;
  align-items: center;
  height: 100vh;
  overflow: hidden;
}

/*裝卡片的容器*/
div.container{
  display: flex; /*讓圖片變成水平排列*/
  width: 90vw; /*會隨著視窗調整寬度*/
}

/* 卡片主體 */
div.card{
 background-position: center;
  background-repeat: no-repeat;
  background-size: cover;
  height: 80vh;
  border-radius: 50px;
  cursor: pointer;
  color: #fff;
  font-weight: bold;
  flex: 0.5;
  margin: 10px;
  position: relative;   /*這樣設是因h3要依照絕對位子擺放*/
  transition: flex 0.7s ease-in;
}

/* 未被展開的圖片標題 */
div.card h3 {
  font-size: 24px;
  position: absolute;
  bottom: 20px;
  left: 20px;
  margin: 0;
  opacity: 0; /*透明度設為0讓它看不到*/
}

/* 展開的圖片 */
div.card.active {
  flex: 5; /*flex是<flex-grow> <flex-shrink> <flex-basis>的縮寫，若只有一個值代表是flex-grow*/
}

/* 展開圖片的標題 */
div.card.active h3 {
  opacity: 1;
  transition: opacity 0.3s ease-in 0.5s; /*讓標題比圖片慢0.5秒進入*/
}

/* 小屏幕下只會有三張圖 */
@media screen and (max-width: 576px) {
  .container {
    width: 100vw;  /*原本是90vw，為了在小屏幕下佔用更多空間所以設100vw*/
  }
  .card:nth-of-type(4),
  .card:nth-of-type(5) {
    display: none;
  }
}
!

JS 

              
                let cards = document.querySelectorAll(".card");
console.log(cards); //NodeList(5)，五個區塊共五個節點
console.log(cards[0]); //div.card.active這個節點
cards.forEach((card) => {
  //箭頭函式中若只有一個參數，可以省略括號( )不寫
  card.addEventListener("click", () => {
    removeActiveClasses(); //把原本的active先移除
    card.classList.add("active"); //再新增active到點擊的圖片上
  });
});

// 移除active
function removeActiveClasses() {
  cards.forEach((card) => {
    card.classList.remove("active");
  });
}
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999px

Console