Show all div if none of link clicked

Question

I have a page name url.com/yourfirstpage/ when i go to the page all the div are hidden by default (display:none) if we target #sec1 as url.com/yourfirstpage/#sec1 it only displays sec1 and hide others. I was wondering if we go the url without having anchor id like url.com/yourfirstpage/ it needs to show all the divs.

#sec1, #sec2, #sec3{
	display:none;
}
#sec1:target{
	display:block;
}
#sec2:target{
	display:block;
}
#sec3:target{
	display:block;
}

<a href="#sec1">sec1</a>
<a href="#sec2">sec2</a>
<a href="#sec3">sec3</a>

<div id="sec1" class="page"> this is sec1</div>
<div id="sec2" class="page"> this is sec2</div>
<div id="sec3" class="page"> this is sec3</div>

Answer 1

Here is a trick in case you are able to modify your HTML structure. The idea is to have the elements visible and then we hide them using :target. Since we don't have previous sibling selector or parent selector, I used id within a parent element to be able to select any element:

#sec1:target .page:nth-child(n+2){
  display: none;
}

#sec2:target .page:nth-child(2n+1){
  display: none;
}

#sec3:target .page:nth-last-child(n+2){
  display: none;
}

<a href="#sec1">sec1</a>
<a href="#sec2">sec2</a>
<a href="#sec3">sec3</a>

<div id="sec1">
  <div id="sec2">
    <div id="sec3">
      <div class="page"> this is sec1</div>
      <div class="page"> this is sec2</div>
      <div class="page"> this is sec3</div>
    </div>
  </div>
</div>

It can work with any number of sections and we can improve the CSS code as follow:

#sec1:target .page:not(:nth-child(1)),
#sec2:target .page:not(:nth-child(2)),
#sec3:target .page:not(:nth-child(3)),
#sec4:target .page:not(:nth-child(4)),
#sec5:target .page:not(:nth-child(5)) {
  display: none;
}

<a href="#sec1">sec1</a>
<a href="#sec2">sec2</a>
<a href="#sec3">sec3</a>
<a href="#sec4">sec4</a>
<a href="#sec5">sec5</a>

<div id="sec1">
  <div id="sec2">
    <div id="sec3">
      <div id="sec4">
        <div id="sec5">
          <div class="page"> this is sec1</div>
          <div class="page"> this is sec2</div>
          <div class="page"> this is sec3</div>
          <div class="page"> this is sec4</div>
          <div class="page"> this is sec5</div>
        </div>
      </div>
    </div>
  </div>
</div>

Answer 2

this quick approach may help

you can do with ! selector in CSS by using postcss plugins

[...document.querySelectorAll('a')].forEach(a => {
    a.addEventListener('click', () => {
        a.parentElement.classList.add('targeted')
    })
})

.targeted div {
  display: none;
}
.targeted div:target {
  display: block;
}

<a href="#sec1">sec1</a>
<a href="#sec2">sec2</a>
<a href="#sec3">sec3</a>

<div id="sec1" class="page"> this is sec1</div>
<div id="sec2" class="page"> this is sec2</div>
<div id="sec3" class="page"> this is sec3</div>