body{
    font-family: Arial;
    margin: 20px; 
}
.container{
    display: flex;
    gap: 10px;
}
.box{
    flex:1;
    background: green;
    color: white;
    text-align: center;
    padding: 20px;
}
@media(max-width:800px){
    .container{
        flex-wrap: wrap;
    } 
    .box{
        flex: 1 1 45%;
    }
}
@media(max-width:500px){ 
    .box{
        flex: 1 1 100%;
    } 
}