Свойство flex-shrink

• 1
• 2
• 3

Исходный код этого примера:

<style>
    ul.flex {
        display: flex;
        justify-content: space-around;
        background: yellowgreen;
        padding: 0;
        margin: 0;
        list-style: none;
    }
    li.flex {
        display: inline-block;
        flex-basis: 300px;
        background: tomato;
        height: 50px;
        margin: 10px;
        line-height: 50px;
        color: white;
        font-weight: bold;
        font-size: 2rem;
        text-align: center;
    }
</style>
<ul class="flex">
    <li class="flex" style="flex-shrink: 1;">1</li>
    <li class="flex" style="flex-shrink: 2;">2</li>
    <li class="flex" style="flex-shrink: 1;">3</li>
</ul>