Responsive website CSS code

responsive website css code

.flexContainer {
    display: flex;
}
.flexItem {
    flex: 1;
}
.flexColumn {
    flex-direction: column;
}
.fullHeight {
    height: 100vh;
}
.whiteBackground {
    background: white;
}
.blueBackground {
    background: lightskyblue;
}
.main{
    order: 2;
    padding: 20px;
    border-left: 1px solid #777777;
    border-right: 1px solid #777777;
}
.sidebar {
    width: 20%;
    background: white;
    padding: 20px;
}
.sidebarLeft{
    order: 1;
}
.sidebarRight{
    order: 3;
}