[Résolu] Création d'un sous-menu pour un menu burger

nav .mynavbar li ul
{
	display: none;
	/* Rend le menu déroulant caché par défaut */
}

nav .mynavbar li:hover ul
{
	/* Affiche le ul contenant le sous-menu au survol de la souris */
	/* Il ne faut pas d'espace entre le li qui déclenche l'affichage du sous-menu et ce ul */
	/* Sinon, quand on déplacera la souris du li vers le sous-menu, on perdra le hover */
	z-index: 99999;
	display: block;
	position: absolute;
	top: 100%;
	float: left;
}

.mynavbar li a:hover
{
	color: #7a6d58;
	transform: scale(1.2);
	opacity: 0.5;
}

*
{
	margin: 0;
	padding: 0;
}

.mynavbar li a
{
	color: yellow;
	text-decoration:none;
}

.container
{
	max-width: 1050px;
	width: 90%;
	margin: auto;
}

.mynavbar
{
	width: 100%;
	box-shadow: 0 1px 4px rgb(146 161 176 / 15%);
	position: fixed;
	z-index: 999999999999999;
	margin-top: 0px;
	display: none;
}

.mynav-container
{
	display: flex;
	justify-content: space-between;
	align-items: center;
	height: 62px;
}

.mynavbar .menu-items
{
	display: flex;
}

.mynavbar .nav-container li
{
	list-style: none;
	list-style-type:none;
}

.mynavbar .nav-container a
{
	text-decoration: none;
	color: #0e2431;
	font-weight: 500;
	font-size: 1.2rem;
	padding: 0.7rem;
	float: left;
	left: 0px;
}

.mynavbar .nav-container a:hover
{
	font-weight: bolder;
	text-decoration:none;
}

.mynav-container
{
	display: block;
	position: relative;
	height: 60px;
	text-decoration:none;
}

.mynav-container .checkbox
{
	position: absolute;
	display: block;
	height: 32px;
	width: 32px;
	top: 20px;
	left: 20px;
	z-index: 5;
	opacity: 0;
	cursor: pointer;
	text-decoration:none;
}

.mynav-container .hamburger-lines
{
	display: block;
	height: 26px;
	width: 32px;
	position: absolute;
	top: 17px;
	left: 20px;
	z-index: 2;
	display: flex;
	flex-direction: column;
	justify-content: space-between;
	color: yellow;
	text-decoration:none;
}

.mynav-container .hamburger-lines .line
{
	display: block;
	height: 4px;
	width: 100%;
	border-radius: 10px;
	background: white;
}

nav .mynav-container .hamburger-lines .line1
{
	transform-origin: 0% 0%;
	transition: transform 0.4s ease-in-out;
}

nav .mynav-container .hamburger-lines .line2
{
	transition: transform 0.2s ease-in-out;
	transition: transform 0.4s ease-in-out;
}

nav .mynav-container .hamburger-lines .line3
{
	transform-origin: 0% 100%;
	transition: transform 0.4s ease-in-out;
}

nav .mynavbar .menu-items
{
	padding-top: 120px;
	box-shadow: inset 0 0 2000px rgba(255, 255, 255, .5);
	height: 100vh;
	width: 80%;
	transform: translate(-150%);
	display: flex;
	flex-direction: column;
	margin-left: 10%;
	margin-right: 10%;
	transition: transform 0.5s ease-in-out;
	text-align: left;
	list-style-type:none;
	text-decoration:none;
	color: white;
	padding-left: 20px;
	line-height: 150%;
	color: yellow;
	text-decoration:none;
}

nav .mynavbar .menu-items li
{
	margin-bottom: 1.2rem;
	font-size: 1rem;
	font-weight: 500;
	color: yellow;
	text-decoration:none;
	text-align: left;
	left: 0px;
}

.mynav-container input[type="checkbox"]:checked ~ .menu-items
{
	transform: translateX(0);
}

.mynav-container input[type="checkbox"]:checked ~ .hamburger-lines .line1
{
	transform: rotate(45deg);
}

.mynav-container input[type="checkbox"]:checked ~ .hamburger-lines .line2
{
	transform: scaleY(0);
}

.mynav-container input[type="checkbox"]:checked ~ .hamburger-lines .line3
{
	transform: rotate(-45deg);
}

.mynav-container input[type="checkbox"]:checked ~ .logo
{
	display: none;
}

.marge_haut
{
	margin-top: -10px;
}

<nav>
	<div class="mynavbar">
		<div class="container mynav-container">
			<input class="checkbox" type="checkbox" name="" id="" />
			<div class="hamburger-lines">
				<span class="line line1"></span>
				<span class="line line2"></span>
				<span class="line line3"></span>
			</div>
			<div class="menu-items">
				<nav>
					<ul class="mynavbar">
						<li>
							<a href="#">Menu1</a>
							<ul>
								<li><a href="#">Drop 1</a></li>
								<li><a href="#">Drop 2</a></li>
								<li><a href="#">Drop 3</a></li>
							</ul>
						</li>
						<br>
						<li><a href="#musette">Rock'n'Roll</a></li>
						<br>
						<li><a href="Contact/formpage.html" target="_blank">Contact</a></li>
					</ul>
				</nav>
			</div>
		</nav>
		<div id="loader">
			<div class="cs-loader">
				<div class="cs-loader-inner">
					<label>?</label>
					<label>?</label>
					<label>?</label>
					<label>?</label>
					<label>?</label>
					<label>?</label>
				</div>
			</div>
		</div>

<nav class="">
      <div class="mynavbar">
        <div class="container mynav-container">
            <input class="checkbox" type="checkbox">
            <div class="hamburger-lines">
              <span class="line line1"></span>
              <span class="line line2"></span>
              <span class="line line3"></span>
			</div>

          <div class="menu-items">
	<nav>
		<ul class="mynavbar">
			<li><a href="#">Menu1</a>
				<ul>
					<li><a href="#">Drop 1</a></li>
					<li><a href="#">Drop 2</a></li>
					<li><a href="#">Drop 3</a></li>
				</ul>
			</li>
			<li><a href="#musette">Rock'n'Roll</a></li>
			<li><a href="Contact/formpage.html" target="_blank">Contact</a></li>
		</ul>
			  </nav>
			</div></div></div>

PLGPPUR a écrit :
Bonjour casper2
qu'est-ce qui empêchait vraiment le bon placement du sous-menu ?