How to make an on-hover bottom border overlap div below? - css

Question

I have a horizontal navigation menu using unordered lists. Under the menu there is a straight gray line which has to have 100% width of the parent container. When hovering the list elements, the part of the line has to be colored blue right under the list element. I can't find any suitable way of doing this. I got it working with position:relative and adding top:14px but it isn't really satisfying me since any changes to the font size or font face will destroy everything. I also thought about changing margins between elements to padding, increasing li's height and giving each one the same gray border and just changing it's color on hover, but I need the line to go all along the parent div's width.
How it has to look:
expected result
My current code:
#container {
width: 80%;
margin: auto;
background-color: white;
}
#container ul {
list-style-type: none;
display: inline-block;
margin: 0;
padding: 0;
margin-top: 5px;
margin-bottom: 10px;
}
#container ul li {
float: left;
margin-left: 20px;
}
#container ul li:first-child {
margin-left: 0;
}
#container ul li a {
text-decoration: none;
color: black;
}
#container ul li a:hover {
color: grey;
}
#container #slider {
display: inline-block;
height: 5px;
background-color: #f1f1f1;
width: 100%;
}
<div id="container">
<ul>
<li>INDEX</li>
<li>HELP</li>
<li>LONG LINK TEXT</li>
</ul>
<span id="slider"></span>
</div>
JSFiddle: https://jsfiddle.net/9fhvyk76/3/

Answer 1

You'll want to use a pseudo element so you have more control over the size/position without really needing to change much. Just add position: relative to the link itself so the pseudo's scale and positioning are associated with it. Let me know if this is what you were looking for!
https://jsfiddle.net/g00jrsqf/
#container ul li a{
position: relative;
}
#container ul li a:after{
content: '';
position: absolute;
display: block;
width: 100%;
height: 4px;
background: #01a2e8;
opacity: 0;
left: 0;
bottom: -29px;
}
#container ul li:hover a:after{
opacity: 1;
}