bootstrap 4 making dropdown scrollable - html

Question

I have a problem with my drop down menu on smaller devices. i cannot make it scroll able when i tried the solution here (that is overflow:auto/ overflow-y:scroll) it's not working even if i use !important. What i'm able to scroll was my main page even if the drop down is open.
<nav class="navbar navbar-toggleable-sm ">
<button class="navbar-toggler navbar-toggler-right main-navbar-toggler" type="button" data-toggle="collapse" data-target="#main-nav-collapse" aria-controls="navbarTogglerDemo02" aria-expanded="false" aria-label="Toggle navigation">
<span class="fa fa-bars"></span>
</button>
<a class="navbar-brand animation" data-animation ="fadeInLeft" href="#"><img src="/093017/img/logo-tmi.png" alt="logo"/></a>
<div class="collapse navbar-collapse" id = "main-nav-collapse" >
<ul class="nav navbar-nav navbar-main mr-auto mt-2 mt-md-0 animation" data-animation = "fadeInRight">
<li class="nav-item dropdown">
<a class="nav-link dropdown-toggle" data-toggle="dropdown" href="#" role="button" aria-haspopup="true" aria-expanded="false">Vehicles</a>
<div class="dropdown-menu default-menu main-menu sm-main-menu animation" data-animation = "fadeIn">
<!-- Nav tabs -->
<div class="sm-main-nav" >
<a class="dropdown-item" href="#">Cars</a><hr>
<a class="dropdown-item" href="#">Vans & Pickup</a><hr>
<a class="dropdown-item" href="#">SUVs & Crossover</a><hr>
<a class="dropdown-item" href="#">MPVs</a><hr>
<a class="dropdown-item" href="#">Hybrid</a><hr>
<a class="dropdown-item" href="#">Performance</a>
</div>
</div>
</li>
<li class="nav-item">
<a class="nav-link " href="#">Owners</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Shop</a>
</li>
<li class="nav-item">
<a class="nav-link " href="#">Promotions</a>
</li>
</ul>
</div>

Answer 1

just you can use #media in your css
#media (max-width: 500px) {
.dropdown-menu{
height:200px;
overflow-y:auto;
}
}

Answer 2

Use max-height instead of height:
.dropdown-menu {
max-height: 200px;
overflow-y: auto;
}

Answer 3

What I can suggest is in place of hard coding height in pixels you can take the advantage of the view port height like adding this style to your dropdown-menu item or add at the class level
Inline
style="overflow-y:auto; max-height:80vh"
For every dropdown
.dropdown-menu {
overflow-y:auto;
max-height:80vh
}

Answer 4

You can use a custom class for scroll bar for dropdown list.
<div class="sm-main-nav customClassForDropDown" >
<a class="dropdown-item" href="#">Cars</a><hr>
<a class="dropdown-item" href="#">Vans & Pickup</a><hr>
<a class="dropdown-item" href="#">SUVs & Crossover</a><hr>
<a class="dropdown-item" href="#">MPVs</a><hr>
<a class="dropdown-item" href="#">Hybrid</a><hr>
<a class="dropdown-item" href="#">Performance</a>
</div>
This is the custom css class.
.customClassForDropDown
{
height: 100px;
overflow-y: auto;
}
check this JSFIDDLE