Shitbox2,
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<style type="text/css">
.container{
display: flex;
flex-wrap: wrap;
width: 200px;
background-color: #696969;
}
.item-filler{
min-width: 0;
flex: 1;
}
.item{
background-color: #FF0000;
margin: 5px;
display: inline-block;
}
.elem {
background-color: #FF0000;
}
.item.item-list {
background-color: #696969;
min-width: 95%;
display: flex;
justify-content: space-between;
flex: 1;
}
</style>
</head>
<body>
<div class="container">
<div class="item">item-1</div>
<div class="item item-list">
<div class="elem">elem-1</div>
<div class="elem">elem-2</div>
<div class="elem">elem-3</div>
</div>
<div class="item item-filler">item-2</div>
<div class="item">item-3</div>
</div>
</body>
</html>