If anyone still needs this, I found this answer . Based on it and on :not pseudo-class, the initial requirement can be accomplished using something like:
div:not(:has(+ .idontwant)) .iwant {
...
}
This approach has an advantage over the general sibling combinator: It also matches backwards, meaning something like:
<div>
<div class="idontwant" />
<div class="iwant" />
</div>
(so if you have the .idontwant element first -> case which would be ignored by the general sibling combinator)
Explanation:
div:has(+ .idontwant) would match any div that has a direct sibling with the class idontwant
div:not(:has(+ .idontwant)) matches any div that doesn't have a direct sibling with class idontwant
- All is left to do is search in the div that doesn't have a direct sibling with the class
idontwant for the class we want.
The selector is quite weird and big, but it does the job, and I think there are (specific) cases where it is quite needed.
Edit (from comments):
If anyone needs to style an element only if it has a specific sibling (or if it doesn't) you can still use the :has Pseudo-class to accomplish it (check snippet):
const toogleHasClassEl = document.getElementById("toogleHasClass")
toogleHasClassEl.onclick = () => toogleHasClassEl.classList.toggle("specificclass")
div:has(.specificclass) .stylethis {
background: orange
}
div:not(:has(.specificclass)) .stylethis {
background: yellow
}
div:has(.stylethis) .specificclass {
background: red
}
<div>
<div class="stylethis">style this</div>
<div id="toogleHasClass" class="specificclass">if this has `specificclass` class (click to toggle)</div>
</div>
<hr/>
<div>
<div class="stylethis">style this different</div>
<div class="thisdoesnthaveclass">if this doesn't have specific class</div>
</div>
<hr/>
<div>
<div class="stylethis">style this different (if alone and therefore doesn't have specific sibling)</div>
</div>