<!doctype html>
<meta charset="utf-8">
<style>
.flex {
display: flex;
flex-direction: column;
}
.grid {
display: grid;
flex-basis: 20px;
border: 1px solid;
}
</style>
<div class="flex">
<div class="grid">
<div style="height: 50px;"></div>
</div>
</div>