Dropdown of Navbar goes behind image slider - html

Question

My dropdown menu goes behind the image slider part of my website. How can I get the dropdown in front of the image slider? I have also some other div's but they go like normally behind the dropdown menu of the Navbar. So I like to have the dropdown in front of the div of the image slider I made. I hope someone can help me
<--code html-->
<nav>
<div class="logo">
<div id="myMenu">
<div class="logo-navbar">
<nav>
<img src="images/logo-groot.png" height="80" />
</nav>
</div>
</div>
</div>
<label for="btn" class="icon">
<span class="fa fa-bars"></span>
</label>
<input type="checkbox" id="btn">
<ul>
<li>Home</li>
<li>
<label for="btn-2" class="show">Assortiment</label>
Assortiment
<input type="checkbox" id="btn-2">
<ul>
<li>Knalvuurwerk</li>
<li>Siervuurwerk</li>
<li>Kindervuurwerk</li>
</ul>
</li>
<li>Contact</li>
</ul>
</nav>
<div class="container">
<h1 id="headline">Nog <span id="days"></span> dagen tot start online vuurwerkverkoop</h1
<div id="countdown">
</div>
</div>
<div class="slideshow-container">
<!-- Full-width images with number and caption text -->
<div class="mySlides fade">
<a href="selectie.html"><img src="images/pyropapel-actie.png" style="width:100%">
</div>
<div class="mySlides fade">
<a href="contact.html"><img src="images/logo-groot.png" style="width:100%">
</div>
<div class="mySlides fade">
<a href="geschiedenis.html"><img src="images/logo-groot.png" style="width:100%">
</div>
<!-- Next and previous buttons -->
<a class="prev" onclick="plusSlides(-1)">❮</a>
<a class="next" onclick="plusSlides(1)">❯</a>
</div>
<br>
<!-- The dots/circles -->
<div class="dots" style="text-align:center">
<span class="dot" onclick="currentSlide(1)"></span>
<span class="dot" onclick="currentSlide(2)"></span>
<span class="dot" onclick="currentSlide(3)"></span>
</div>
</div>
<-- css -->
nav{
background: #151515;
}
nav:after{
content: '';
clear: both;
display: table;
}
nav .logo{
float: left;
line-height: 70px;
padding-left: 60px;
}
nav ul{
float: right;
margin-right: 4px;
list-style: none;
position: relative;
}
nav ul li{
float: left;
display: inline-block;
background: #151515;
margin: 5 5px;
}
nav ul li a{
color: white;
line-height: 70px;
text-decoration: none;
font-size: 18px;
padding: 8px 15px;
}
nav ul li a:hover{
color: white;
border-radius: 5px;
box-shadow: 0 0 5px #000000,
0 0 10px #0a0a0a;
}
nav ul ul li a:hover{
box-shadow: none;
}
nav ul ul{
position: absolute;
top: 90px;
border-top: 3px solid red;
opacity: 0;
visibility: hidden;
transition: top .3s;
}
nav ul ul ul{
border-top: none;
}
nav ul li:hover > ul{
top: 70px;
opacity: 1;
visibility: visible;
}
nav ul ul li{
position: relative;
margin: 0px -20px;
width: 175px;
float: none;
display: list-item;
border-bottom: 1px solid rgba(0,0,0,0.3);
text-align:center;
}
nav ul ul li a{
line-height: 50px;
}
nav ul ul ul li{
position: relative;
top: -60px;
left: 150px;
}
.show,.icon,input{
display: none;
}
.fa-plus{
font-size: 15px;
margin-left: 40px;
}
#media all and (max-width: 968px) {
nav ul{
margin-right: 0px;
float: left;
}
nav .logo{
padding-left: 30px;
width: 100%;
}
.show + a, nav > ul{
display: none;
}
nav ul li,nav ul ul li{
display: block;
width: 100%;
}
nav ul li a:hover{
box-shadow: none;
}
.show{
display: block;
color: white;
font-size: 18px;
padding: 0 15px;
line-height: 70px;
cursor: pointer;
}
.show:hover{
color: white;
border-radius:5px;
}
.icon{
display: block;
color: white;
position: absolute;
top: 25;
right: 40px;
line-height: 70px;
cursor: pointer;
font-size: 25px;
}
nav ul ul{
top: 70px;
border-top: 0px;
float: none;
position: static;
display: none;
opacity: 1;
visibility: visible;
}
nav ul ul a{
padding-left: 40px;
}
nav ul ul ul a{
padding-left: 80px;
}
nav ul ul ul li{
position: static;
}
[id^=btn]:checked + ul{
display: block;
}
nav ul ul li{
border-bottom: 0px;
}
span.cancel:before{
content: '\f00d';
}
}
.slideshow-container {
position: relative;
margin: auto;
background-color: rgba(0, 0, 0, 1);
width:75%;
}
/* Hide the images by default */
.mySlides {
display: none;
}
/* Next & previous buttons */
.prev, .next {
cursor: pointer;
position: absolute;
align-items: center;
top: 50%;
width:auto;
margin-top: -22px;
padding: 16px;
color: white;
font-weight: bold;
font-size: 18px;
transition: 0.6s ease;
border-radius: 0 3px 3px 0;
user-select: none;
}
/* Position the "next button" to the right */
.next {
right: 0;
border-radius: 3px 0 0 3px;
}
/* On hover, add a black background color with a little bit see-through */
.prev:hover, .next:hover {
background-color: rgba(0,0,0,0.8);
}
/* Caption text */
.text {
color: #f2f2f2;
font-size: 15px;
padding: 8px 12px;
position: absolute;
bottom: 8px;
width: 100%;
text-align: center;
}
/* Number text (1/3 etc) */
.numbertext {
color: #f2f2f2;
font-size: 12px;
padding: 8px 12px;
position: absolute;
top: 0;
}
/* The dots/bullets/indicators */
.dot {
cursor: pointer;
height: 15px;
width: 15px;
margin: 0 2px;
border-radius: 50%;
display: inline-block;
transition: background-color 0.6s ease;
background-color: #bbb;
}
.active, .dot:hover {
background-color: #717171;
}
.dots{
background-color: rgba(23, 14, 13, 0.97);
width:75%;
align-items:center;
margin:auto;
padding-top: 20px;
margin-top:-24px;
}
/* Fading animation */
.fade {
-webkit-animation-name: fade;
-webkit-animation-duration: 1.5s;
animation-name: fade;
animation-duration: 1.5s;
}
#-webkit-keyframes fade {
from {opacity: .4}
to {opacity: 1}
}
#keyframes fade {
from {opacity: .4}
to {opacity: 1}
}