korifey,
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<style>
#b1,#b4,#b5,#b6,#b3,#b2{width:50px;height:30px;background-color:brown;cursor:pointer;float:left;margin-right:5px;text-align:center;padding-top:10px}
.cat-all,.mcat-all,.misk,.men1,.msor,.isk{width:300px;height:100px;border:1px solid #000000;display:none;text-align:center;padding-top:50px}
div.open {
display: block;
}
</style>
</head>
<body>
<div id="b3"><div>b3</div></div>
<div id="b2">b2</div>
<div id="b1">b1</div>
<div id="b4"><span>b4</span></div>
<div id="b5">b5</div>
<div id="b6">b6</div>
<br><br><br>
<div class="isk">block button 1</div>
<div class="mcat-all">block button 2</div>
<div class="misk">block button 3</div>
<div class="men1">block button 4</div>
<div class="cat-all">block button 5</div>
<div class="msor">block button 6</div>
<script>
let open;
const rels=[['#b3','.isk'],['#b2','.mcat-all'],['#b1','.misk'],['#b4','.men1'],['#b5','.cat-all'],['#b6','.msor']];
addEventListener( 'click' , ({target}) => {
if(target.closest('.open')) return;
let item = rels.find(([selector, ..._]) => target.closest(selector));
if(item) {
item = document.querySelector(item[1]);
if(!item) return;
item.classList.toggle('open');
}
if(open && open != item) open.classList.remove('open');
open = item;
})
</script>
</body>
</html>