Possible to have one border overlap/cancel out another border? - html

Question

I have two lists sitting side-by-side. In the full code there will be the ability to select one of the list items from the MainList which will show the relevant list items from the SubList. What I would like is for the border-right of the MainList to overlap the border-left of the SubList to make it look like the SubList items are being shown as a result of the selection in the MainList.
ul {
list-style: none;
}
.BigContainer {
border: 2px solid #d50f67;
border-radius: 5px;
margin: 10px 0;
padding: 5px;
overflow: auto;
}
.MainListContainer {
width: 50%;
float: left;
}
.MainListItem {
border-bottom: 1px solid #ddd;
border-right: 1px solid white;
padding: 5px;
z-index: 2;
}
.MainListItem:last-of-type {
border: none;
}
.SubListContainer {
width: 45%;
float: left;
border: 1px solid #ddd;
border-radius: 5px;
}
.SubListItem {
padding: 5px;
z-index: 1;
}
<div class="BigContainer">
<div class="MainListContainer">
<ul class="MainList">
<li class="MainListItem">List Option A</li>
<li class="MainListItem">List Option B</li>
<li class="MainListItem">List Option C</li>
</ul>
</div>
<div class="SubListContainer">
<ul class="SubList">
<li class="SubListItem">Sub-Option 1</li>
<li class="SubListItem">Sub-Option 2</li>
<li class="SubListItem">Sub-Option 3</li>
<li class="SubListItem">Sub-Option 4</li>
<li class="SubListItem">Sub-Option 5</li>
</ul>
</div>
</div>
So, the border-right of the MainList would be white/transparent to basically erase a portion of the SubList border. I appreciate that, at the moment, making this happen would remove more of the SubList border than desired, but I will code the selection process properly to ensure only the selected item has the relevant border styling applied.

Answer 1

Add selected class to the selected item, then add
.selected:after{
content:"";
position: absolute;
right:-2px;
top:0;
width: 1px;
height: 100%;
background-color: white;
}
This will be placed right where you want it to. Note that MainListItem needs to have a position: relative; for the position to work.
.selected:after{
content:"";
position: absolute;
right:-2px;
top:0;
width: 1px;
height: 100%;
background-color: white;
}
ul {
list-style: none;
}
.BigContainer {
border: 2px solid #d50f67;
border-radius: 5px;
margin: 10px 0;
padding: 5px;
overflow: auto;
}
.MainListContainer {
width: 50%;
float: left;
}
.MainListItem {
border-bottom: 1px solid #ddd;
border-right: 1px solid white;
padding: 5px;
z-index: 2;
position: relative;
}
.MainListItem:last-of-type {
border: none;
}
.SubListContainer {
width: 45%;
float: left;
border: 1px solid #ddd;
border-radius: 5px;
}
.SubListItem {
padding: 5px;
z-index: 1;
}
<div class="BigContainer">
<div class="MainListContainer">
<ul class="MainList">
<li class="MainListItem">List Option A</li>
<li class="MainListItem selected">List Option B</li>
<li class="MainListItem">List Option C</li>
</ul>
</div>
<div class="SubListContainer">
<ul class="SubList">
<li class="SubListItem">Sub-Option 1</li>
<li class="SubListItem">Sub-Option 2</li>
<li class="SubListItem">Sub-Option 3</li>
<li class="SubListItem">Sub-Option 4</li>
<li class="SubListItem">Sub-Option 5</li>
</ul>
</div>
</div>