Swap DIV position with CSS only

Someone linked me this: What is the best way to move an element that's on the top to the bottom in Responsive design.

The solution in that worked perfectly. Though it doesn’t support old IE, that doesn’t matter for me, since I’m using responsive design for mobile. And it works for most mobile browsers.

Basically, I had this:

@media (max-width: 30em) {
  .container {
    display: -webkit-box;
    display: -moz-box;
    display: -ms-flexbox;
    display: -webkit-flex;
    display: flex;
    -webkit-box-orient: vertical;
    -moz-box-orient: vertical;
    -webkit-flex-direction: column;
    -ms-flex-direction: column;
    flex-direction: column;
    /* optional */
    -webkit-box-align: start;
    -moz-box-align: start;
    -ms-flex-align: start;
    -webkit-align-items: flex-start;
    align-items: flex-start;
  }

  .container .first_div {
    -webkit-box-ordinal-group: 2;
    -moz-box-ordinal-group: 2;
    -ms-flex-order: 2;
    -webkit-order: 2;
    order: 2;
  }

  .container .second_div {
    -webkit-box-ordinal-group: 1;
    -moz-box-ordinal-group: 1;
    -ms-flex-order: 1;
    -webkit-order: 1;
    order: 1;
  }
}

This worked better than floats for me, because I needed them stacked on top of each other and I had about five different divs that I had to swap around the position of.

The accepted answer worked for most browsers but for some reason on iOS Chrome and Safari browsers the content that should have shown second was being hidden. I tried some other steps that forced content to stack on top of each other, and eventually I tried the following solution that gave me the intended effect (switch content display order on mobile screens), without bugs of stacked or hidden content:

.container {
  display:flex;
  flex-direction: column-reverse;
}

.section1,
.section2 {
  height: auto;
}