.contenedor{
    background: lightblue;
    height: 700px;
    display: flex;
}

#elemento1 {
    flex-basis: 10%;
}

#elemento2 {
    flex-basis:  20%;
}

#elemento3 {
    flex-basis: 70%;
}

.elemento{
    background: pink;
    width: 120px;
    height: 120px;
    font-size: 4rem;
    text-align: center;
    border: 2px solid black;


}