#bf20_menu {width:100%;
height:50px;
background-color:#262626;
border-bottom:1px solid rgb(255, 255, 255, .2);
margin-top:100px;
}
#bf20_menu > ul {text-align:center;
width:100%;
height:inherit;
display:flex;
justify-content: center;
margin:0 auto;}
.bf20_menu_li {float:left;
list-style-type:none;
color:white;
width:15%;
height:100%;
display: inline-block;
border-left:1px solid rgb(255, 255, 255, .2);
box-sizing: border-box;
padding-top:15px;}
#bf20_menu > ul > li:nth-child(4) {border-right:1px solid rgb(255, 255, 255, .2);}
#bf20_menu > ul > li > a {color:white;
font-weight:400;
width: 100%;
display: block;}
@media screen and (max-width: 1120px) {.bf20_menu_li { width:25%; } }
#bf20_hoverbox { background-color: gray;
display: inline-block;
position: absolute;
top: 64%;
padding: 5px 15px;
border-radius: 15px;
left: 70%;
transition:all 1s;
display:none;}
#bf20_hover + #bf20_hoverbox{
display:block;
}
#bf20_hover #bf20_hoverbox{
display:block;
}
<div id="bf20_menu">
<ul>
<li class="bf20_menu_li bf20_menu_li_active"><a href="#bf20_menu_href1">test1</a></li>
<li class="bf20_menu_li"><a href="#bf20_menu_href2">test2</a></li>
<li class="bf20_menu_li"><a href="#bf20_menu_href3">test3</a></li>
<li class="bf20_menu_li" id="bf20_hover"><a href="#bf20_menu_href4">hover this!</a></li>
</ul>
<p id="bf20_hoverbox">something</p>
</div>
i wanna make hidden div box (id name is "bf20_hoverbox") is appear when i hover li (id name is "bf20_hover") so i searched it on google and tried the solution but not worked in my code. even if i do exactly same.. as you can see in my css at the last. i used "+" " ", cause i saw this is the solution in stack overflow. which is totally not work in my code;;; dont know the reason;;
any help will be so appreciate! thanks!!