I think the traditional way is flexible and fairly easy to understand:
Markup
<div class="flex-grid">
<div class="col-4">.col-4</div>
<div class="col-4">.col-4</div>
<div class="col-4">.col-4</div>
<div class="col-4">.col-4</div>
<div class="col-4">.col-4</div>
<div class="col-4">.col-4</div>
<div class="col-3">.col-3</div>
<div class="col-9">.col-9</div>
<div class="col-6">.col-6</div>
<div class="col-6">.col-6</div>
</div>
Create grid.css file:
.flex-grid {
display: flex;
flex-flow: wrap;
}
.col-1 {flex: 0 0 8.3333%}
.col-2 {flex: 0 0 16.6666%}
.col-3 {flex: 0 0 25%}
.col-4 {flex: 0 0 33.3333%}
.col-5 {flex: 0 0 41.6666%}
.col-6 {flex: 0 0 50%}
.col-7 {flex: 0 0 58.3333%}
.col-8 {flex: 0 0 66.6666%}
.col-9 {flex: 0 0 75%}
.col-10 {flex: 0 0 83.3333%}
.col-11 {flex: 0 0 91.6666%}
.col-12 {flex: 0 0 100%}
[class*="col-"] {
margin: 0 0 10px 0;
-webkit-box-sizing: border-box;
-moz-box-sizing: border-box;
box-sizing: border-box;
}
@media (max-width: 400px) {
.flex-grid {
display: block;
}
}
I've created an example (jsfiddle)
Try to resize the window under 400px, it's responsive!!