estilo.css

.total {
    overflow: auto;
}

#principal {
    margin-left: 4px;
}

#barraLateral {
    float: none;
    width: auto
}

#menu {
    margin: 0;
    padding: 0;
}

.item {
    background: rosybrown;
    border: 3px solid violet;
    border-radius: 4px;
    list-style-type: none;
    margin: 4px;
    padding: 2px;
}

@media screen and (min-width: 350px){
    #barraLateral {
        float: left;
        width: 200px;
    }
    #principal {
        margin-left: 180px;
    }

}