You can set the maximum width for an element to 50%. This will maintain almost the same width, no matter what. I say almost because your borders are also set.
For the width to be the same, you also need to set the window size: border-box for the element.
So your code will be:
.item { border: 1px dashed blue; height: 50px; box-sizing: border-box; max-width: 50%; }
.container { border: 1px solid red; height: 300px; display: flex; flex-direction: column; justify-content: flex-start; flex-wrap: wrap; } .item { border: 1px dashed blue; height: 50px; box-sizing: border-box; max-width: 50%; }
<div class="container"> <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>
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