<style>.menu > h3{
background-color: red;
}
</style>

you want to look up your css selectors https://www.w3schools.com/cssref/css_selectors.asp this is a good place to go for reference

I think your question needs more context… but anyways, the most efficient way IS to add a class to each of the h3 elements, but you could also access the h3 of the div like so

     <style>
     .main h3 {
     /*add property here*/
    }
    </style>
    <div class = "main">
   <h3 class="menu">Home</h3>
   <h3 class="menu">About</h3>
   <h3 class="menu">My work</h3>
   <h3 class="menu">Contact me</h3>
   <h3 class="menu">Reviews</h3>
   </div>

Now whatever property that’ll be added to .main h3 will only be applied to the h3 elements inside the main div.

I want to apply a styling property to multiple h3 elements grouped in a div. I don’t want to apply the property to the div itself but to each of its elements. I know I can use class for each of them but that does not seem too efficient, also I don’t want to apply the property to the h3 tag because I will probably use it later with a different style.

h3 {
  display: inline;
}
.menu {
  background-color: red;
}

<div class="menu">
  <h3>Home</h3>
  <h3>About</h3>
  <h3>My work</h3>
  <h3>Contact me</h3>
  <h3>Reviews</h3>
</div>

I want something like this instead:

h3 {
  display: inline;
}
.menu {
  background-color: red;
}

<div>
  <h3 class="menu">Home</h3>
  <h3 class="menu">About</h3>
  <h3 class="menu">My work</h3>
  <h3 class="menu">Contact me</h3>
  <h3 class="menu">Reviews</h3>
</div>