Target the first element only if it has other siblings

Question

Without adding any classes (or touching the HTML) is there a way to target the first element inside a div ONLY if there is a second element in that div? Below is my HTML:

<div class="grid">
    <div class="content">I WANT TO APPLY CSS TO THIS</div>
    <div class="content">But only if there is 2nd .content element in the same parent element</div>
</div>
<div class="grid">
    <div class="content">Don't apply here</div>
</div>
<div class="grid">
    <div class="content">Don't apply here</div>
</div>
<div class="grid">
    <div class="content">I WANT TO APPLY CSS TO THIS</div>
    <div class="content">But only if there is 2nd .content element in the same parent element</div>
</div>

A few context to this for a better picture ... I want to center the .content if it's the only .content inside .grid. But if there are two .content divs, then I want them to float next to each other.

Note:

I already know I can target the second .content by

.grid .content:nth-child(2) { ... }

Answer 1

.grid > .content:first-child:not(:only-child) {
    color: blue;
}

<div class="grid">
    <div class="content">I WANT TO APPLY CSS TO THIS</div>
    <div class="content">But only if there is 2nd .content element in the same parent element</div>
</div>
<div class="grid">
    <div class="content">Don't apply here</div>
</div>
<div class="grid">
    <div class="content">Don't apply here</div>
</div>
<div class="grid">
    <div class="content">I WANT TO APPLY CSS TO THIS</div>
    <div class="content">But only if there is 2nd .content element in the same parent element</div>
</div>

:first-child:not(:only-child) would be your selector.