<div class="flexbox-demo flexbox-area1"><div class="container1">1</div><div class="container2">2</div></div>
.flexbox-demo {display:flex;}
<div class="flexbox-demo flexbox-area2"><div class="container1">1</div><div class="container2">2</div><div class="container3">3</div></div>
.flexbox-demo {display:flex;}
<div class="flexbox-demo flexbox-area3"><div class="container1">1</div><div class="container2">2</div><div class="container3">3</div></div>
.flexbox-demo {display:flex;}
.flexbox-area3 .container1 {flex:1;}
.flexbox-area3 .container2 {flex:2;}
.flexbox-area3 .container3 {flex:1;}
<div class="flexbox-demo flexbox-area4"><div class="container1">1</div><div class="container2">2</div><div class="container3">3</div></div>
.flexbox-demo {display:flex;}
.flexbox-area4 .container1 {flex:1;order:2;}
.flexbox-area4 .container2 {flex:2;order:3;}
.flexbox-area4 .container3 {flex:1;order:1;}
<div class="flexbox-demo flexbox-area5"><div class="container1">1</div><div class="container2">2</div><div class="container3">3</div><div class="container4">4</div><div class="container5">5</div><div class="container6">6</div><div class="container7">7</div><div class="container8">8</div><div class="container9">9</div></div>
.flexbox-demo {display:flex;}
.flexbox-area5 {flex-wrap:wrap;}
.flexbox-area5 [class^="container"] {flex:1;}