Make it create scrollbar when two components collide

Question

For example, I have two Ivs on the page, and they are set to width and height, but when they crash I would like me to instead of either go down or go up, just appear a scroll bar.

Answer 1

I made an example using box-flex, I don’t know what your case is, but it follows below:

.pagina {
  overflow: auto;
  display: -webkit-box;
  display: -moz-box;
}
.esquerda {
  background-color: red;
  width: 100%;
}
.direita {
  background-color: blue;
  width: 100%;
}

<div class="pagina">
  <div class="esquerda">
    a
  </div>
  <div class="direita">
    b
  </div>
</div>