.flex{
background:red;
padding:5px;
display:flex;
flex-direction: column;
height:200px;
overflow: auto;
}
.up{
background:blue;
}
.down{
background:green;
width:100%;
height:50px;
flex-basis:50px;
}
.block{
font-size:20px;
padding:30px;
margin:10px;
background:brown;
}
<div class="flex">
<div class="up">
<div class="block">dd</div>
<div class="block">dd</div>
<div class="block">dd</div>
</div>
<div class="down"></div>
</div>