CSSプロパティのz-indexとorderは整数でしか使用不可

HTML

<div class="test">
  <div class="test12">z-index: 1.2</div>
  <div class="test11">z-index: 1.1</div>
</div>
<div class="content">
  <div class="box1">box1</div>
  <div class="box2">box2</div>
</div>

CSS

.test {
  position: relative;
  width: 100px;
  height: 100px;
  margin-bottom: 10px;
  background: #EEE;
}
.test11,
.test12 {
  position: absolute;
  width: 80px;
  height: 80px;
}
.test11 {
  top: 0;
  left: 0;
  background: red;
  z-index: 1.1;
}
.test12 {
  right: 0;
  bottom: 0;
  background: blue;
  z-index: 1.2;
}
.content {
  display: flex;
  width: 100px;
  height: 100px;
  background: #EEE;
}
.box1,
.box2 {
  width: 50px;
  height: 50px;
}
.box1 {
  background: orange;
  order: 1.2;
}
.box2 {
  background: green;
  order: 1.1;
}