.bigbox{
    display: grid;
    grid-template-columns: 25% 25% auto;
    grid-template-rows: auto auto auto;
    grid-gap: 1em;
    padding: 1em;
    border: 2px solid yellowgreen;
}
.box{
    width: 100%;
    height: 150px;
    background-color: yellowgreen;
}