可以在css文件中为card的div类使用min-height:...属性

.card-container {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
}

.card {
  background-color: #fff;
  box-shadow: 0 4px 8px 0 rgba(0,0,0,0.2);
  padding: 20px;
  margin-bottom: 20px;
  flex-basis: calc(33.33% - 20px);
}

<div class="card-container">
  <div class="card">
    <h3>Card 1</h3>
    
  </div>
  <div class="card">
    <h3>Card 2</h3>
    
    
  </div>
  <div class="card">
    <h3>Card 3</h3>
    
  </div>
</div>

正如你所说，你不能使用弹性，尝试使用以下方法之一：
1.使用display: table和display: table-cell属性显示表

.card-group {
    display: table;
    width: 100%;
    table-layout: fixed;
    border-collapse: separate;
    border-spacing: 10px;
}

.card {
    display: table-cell;
    vertical-align: top;
    width: 33.33%;
    background-color: #fff;
    padding: 10px;
    border: 1px solid #ccc;
}

<div class="slider">
    <div class="card-group">
        <div class="card">
            <h1>Where was it consumed the most?</h1>
            Lorem ipsum dolor sit amet, consectetur adipisicing elit. Accusantium ad adipisci architecto consequatur,
            corporis, cupiditate deleniti distinctio illo iste magni nihil odit officia porro quidem reiciendis
            reprehenderit similique voluptate voluptates.
        </div>
        <div class="card">
            <h1>Where was it eaten the most?</h1>
            Lorem ipsum dolor sit amet, consectetur adipisicing elit.
        </div>
    </div>
</div>

1.使用display: grid、grid-template-columns、grid-gap的网格显示：

.card-group {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    grid-gap: 10px;
}

.card {
    background-color: #fff;
    padding: 10px;
    border: 1px solid #ccc;
}

<div class="slider">
    <div class="card-group">
        <div class="card">
            <h1>Where was it consumed the most?</h1>
            Lorem ipsum dolor sit amet, consectetur adipisicing elit. Accusantium ad adipisci architecto consequatur,
            corporis, cupiditate deleniti distinctio illo iste magni nihil odit officia porro quidem reiciendis
            reprehenderit similique voluptate voluptates.
        </div>
        <div class="card">
            <h1>Where was it eaten the most?</h1>
            Lorem ipsum dolor sit amet, consectetur adipisicing elit.
        </div>
    </div>
</div>

他们都做同样的高度，但在不同的方式，看看什么方法会更好地在您的项目。