Why using grid-template-areas with grid areas of the same class but different selectors are displayed in reverse order?

Question

I am using css grid and I am experiencing a weird issue.

As you can see in the code below. I have a parent grid, homepage__section__medical-types__content which declares the

grid-template-areas:
    "blue"
    "content1"
    "green"
    "content2";

and four rows. content1 and content2 are assigned respectively to:

homepage__heading__info:first-child

and

homepage__heading__info:nth-child(2)

but why are they displayed in reverse order as they are declared? What am I doing wrong?

body {
  margin: 0;
  display: flex;
  justify-content: center;
}

.container {
  background-color: lavenderblush;
  height: auto;
  width: 320px;
}

.homepage__section__medical-types {
  display: grid;
  grid-template-areas: ". medic .";
  grid-template-columns: 48px 1fr 16px;
}

.homepage__section__medical-types__content {
  grid-area: medic;
  display: grid;
  grid-template-areas:
		"blue"
		"content1"
		"green"
		"content2";
  grid-template-rows: 250px 1fr 250px 1fr;
}

.homepage__heading-box {
  height: 100%;
  border-radius: 25px;
}

.homepage__heading-box--blue {
  grid-area: blue;
  background-image: linear-gradient(to bottom, #669DD6, #ADDAF1);
}

.homepage__heading-box--green {
  grid-area: green;
  background-image: linear-gradient(to bottom, #51CEA2, #97DCC6);
}

.homepage__heading__info {
  background-color: aliceblue;
}

.homepage__heading__info:first-child {
  grid-area: content1;
}

.homepage__heading__info:nth-child(2) {
  grid-area: content2;
  color: red
}

<div class="container">
  <div class="homepage__section__medical-types">
    <div class="homepage__section__medical-types__content">
      <div class="homepage__heading-box homepage__heading-box--blue"></div>
      <div class="homepage__heading__info">
        <p>1</p>
      </div>
      <div class="homepage__heading-box homepage__heading-box--green"></div>
      <div class="homepage__heading__info">
        <p>2</p>
      </div>
    </div>
  </div>
</div>

EDIT: I have noticed that just commenting out grid-area: content1; and grid-area: content2; but keeping the same the parent grid-template-area, the corresponding elements are displayed in the correct order. I am more confused then before.

Answer 1

You are misinterpreting the purpose of the nth-child() pseudo-class.

To be clear, this is your HTML:

<div class="homepage__section__medical-types__content">
   <div class="homepage__heading-box homepage__heading-box--blue"></div>
   <div class="homepage__heading__info"><p>1</p></div>
   <div class="homepage__heading-box homepage__heading-box--green"></div>
   <div class="homepage__heading__info"><p>2</p></div>
</div>

And this is your CSS:

.homepage__heading__info:first-child {
   grid-area: content1;
}

.homepage__heading__info:nth-child(2) {
   grid-area: content2;
   color: red
}

So, :first-child applies to the first child among all siblings. .homepage__heading__info is never the first child among all siblings. So with :first-child applied, it is simply ignored. If you search for this selector in dev tools, it doesn't even appear, because its target doesn't exist.

With .homepage__heading__info:nth-child(2), this actually applies to the second child among all siblings, which happens to be the first .homepage__heading__info (the item with text "1"). The selector applies grid area "content2" to this element, sending it to the bottom, as per grid-template-areas.

grid-template-areas:
   "blue"
   "content1"
   "green"
   "content2"

The element with text "2" is auto-placed in the unoccupied row, which happens to be row 2 (again, content1 doesn't exist). As a result, 2 comes before 1.

---

EDIT: I have noticed that just commenting out grid-area: content1 and grid-area: content2 but keeping the same the parent grid-template-area, the corresponding elements are displayed in the correct order. I am more confused then before.

Without the grid areas, the algorithm places the specified items per grid-template-areas (in this case, that would be only "blue" and "green") and the remaining items are auto-placed into existing rows in source order.