use flex in container with multiple components
.wrap {
display: flex;
flex-wrap: wrap;
flex-direction: column; /* NEW */
height: 100px; /* NEW */
justify-content: space-between; /* NEW */
}
.elem1 {
width: 20%;
flex-basis: 100%; /* NEW */
border: 1px solid red;
}
.elem2,
.elem3 {
width: 75%;
flex-basis: 40%; /* NEW */
border: 1px solid red;
}