*{
    box-sizing: border-box;
}
body{
    margin: 0;
    background-color: lightgrey;
    line-height: 1,4;
}
.container{
    max-width: 960px;
    margin: 0 auto;
}
.row{
    display: flex;
}
.flex-item{
    flex-basis: 300px;
}
.prvi{
    background-color: red;
    flex-grow: 1;
}
.dva{
    background-color: lightblue;
    flex-grow: 4;
}
.tri{
    background-color: purple;
    flex-grow: 7;
}
.prvi {
    background-color: red;
    flex-shrink: 1;
}
.drugi{
    background-color: lightblue;
    flex-shrink: 2;
}
.treci{
    background-color: purple;
    flex-shrink: 4;
}