Sub menu not following main menu when scrolling horizontally - css

Question

All works fine but if you make the window smaller and scroll the menu horizontally the submenu is out of alignment with its parent:
https://jsfiddle.net/9hjgo1qc/7/
Any thoughts on how to make the submenu follow the main menu on scrolling?
HTML
<div class="navbar">
<div class="dropdown">
<button class="nav_button">M1</button>
</div>
<div class="dropdown">
<button class="nav_button">M2</button>
<div class="dropdown-content">
<button class="menu_sub_button">M2-1</button>
<button class="menu_sub_button">M2-2</button>
</div>
</div>
<div class="dropdown">
<button class="nav_button">M3</button>
</div>
<div class="dropdown">
<button class="nav_button">M4</button>
</div>
</div>
More text
CSS
.navbar {
width:100%;
overflow-x: auto;
overflow-y: hidden;
font-family: Arial, Helvetica, sans-serif;
white-space: nowrap;
}
.navbar button {
font-size: 12px;
color: black;
text-align: center;
text-decoration: none;
}
.dropdown {
overflow: auto;
min-width: 180px;
display: inline-block;
}
.dropdown-content {
display: none;
position: absolute;
background-color: #f9f9f9;
min-width: 180px;
box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
z-index: 1;
}
.dropdown:hover .dropdown-content {
display: block;
}
.nav_button {
white-space: normal;
width: 175px;
height: 30px;
display: block;
text-align: left;
color: black;
border-style: none;
background-color: #757BD3;
}
.menu_sub_button {
white-space: normal;
width: 175px;
height: 25px;
display: block;
text-align: left;
color: black;
border-style: none;
background-color: #D8D8D8;
}
.menu_sub_button:hover {
background-color: #C3C3C3;
}

Answer 1

I have improved your code, it works well on the desktop and on the Smartphone
$("#cssmenu").menumaker({
title: "Menu",
breakpoint: 768,
format: "multitoggle"
});
#import url(https://fonts.googleapis.com/css?family=Montserrat:400,700);
#cssmenu,
#cssmenu ul,
#cssmenu ul li,
#cssmenu ul li a,
#cssmenu #menu-button {
margin: 0;
padding: 0;
border: 0;
list-style: none;
line-height: 1;
display: block;
position: relative;
-webkit-box-sizing: border-box;
-moz-box-sizing: border-box;
box-sizing: border-box;
}
#cssmenu:after,
#cssmenu > ul:after {
content: ".";
display: block;
clear: both;
visibility: hidden;
line-height: 0;
height: 0;
}
#cssmenu #menu-button {
display: none;
}
#cssmenu {
font-family: Montserrat, sans-serif;
background: #757bd3;
}
#cssmenu > ul > li {
float: left;
}
#cssmenu.align-center > ul {
font-size: 0;
text-align: center;
}
#cssmenu.align-center > ul > li {
display: inline-block;
float: none;
}
#cssmenu.align-center ul ul {
text-align: left;
}
#cssmenu.align-right > ul > li {
float: right;
}
#cssmenu > ul > li > a {
padding: 17px;
font-size: 12px;
letter-spacing: 1px;
text-decoration: none;
color: #dddddd;
font-weight: 700;
text-transform: uppercase;
}
#cssmenu > ul > li:hover > a {
color: #ffffff;
}
#cssmenu > ul > li.has-sub > a {
padding-right: 30px;
}
#cssmenu > ul > li.has-sub > a:after {
position: absolute;
top: 22px;
right: 11px;
width: 8px;
height: 2px;
display: block;
background: #dddddd;
content: '';
}
#cssmenu > ul > li.has-sub > a:before {
position: absolute;
top: 19px;
right: 14px;
display: block;
width: 2px;
height: 8px;
background: #dddddd;
content: '';
-webkit-transition: all .25s ease;
-moz-transition: all .25s ease;
-ms-transition: all .25s ease;
-o-transition: all .25s ease;
transition: all .25s ease;
}
#cssmenu > ul > li.has-sub:hover > a:before {
top: 23px;
height: 0;
}
#cssmenu ul ul {
position: absolute;
left: -9999px;
}
#cssmenu.align-right ul ul {
text-align: right;
}
#cssmenu ul ul li {
height: 0;
-webkit-transition: all .25s ease;
-moz-transition: all .25s ease;
-ms-transition: all .25s ease;
-o-transition: all .25s ease;
transition: all .25s ease;
}
#cssmenu li:hover > ul {
left: auto;
}
#cssmenu.align-right li:hover > ul {
left: auto;
right: 0;
}
#cssmenu li:hover > ul > li {
height: 35px;
}
#cssmenu ul ul ul {
margin-left: 100%;
top: 0;
}
#cssmenu.align-right ul ul ul {
margin-left: 0;
margin-right: 100%;
}
#cssmenu ul ul li a {
border-bottom: 1px solid rgba(150, 150, 150, 0.15);
padding: 11px 15px;
width: 170px;
font-size: 12px;
text-decoration: none;
color: #000000;
font-weight: 400;
background: #d8d8d8;
}
#cssmenu ul ul li:last-child > a,
#cssmenu ul ul li.last-item > a {
border-bottom: 0;
}
#cssmenu ul ul li:hover > a,
#cssmenu ul ul li a:hover {
color: #ffffff;
}
#cssmenu ul ul li.has-sub > a:after {
position: absolute;
top: 16px;
right: 11px;
width: 8px;
height: 2px;
display: block;
background: #000000;
content: '';
}
#cssmenu.align-right ul ul li.has-sub > a:after {
right: auto;
left: 11px;
}
#cssmenu ul ul li.has-sub > a:before {
position: absolute;
top: 13px;
right: 14px;
display: block;
width: 2px;
height: 8px;
background: #000000;
content: '';
-webkit-transition: all .25s ease;
-moz-transition: all .25s ease;
-ms-transition: all .25s ease;
-o-transition: all .25s ease;
transition: all .25s ease;
}
#cssmenu.align-right ul ul li.has-sub > a:before {
right: auto;
left: 14px;
}
#cssmenu ul ul > li.has-sub:hover > a:before {
top: 17px;
height: 0;
}
#cssmenu.small-screen {
width: 100%;
}
#cssmenu.small-screen ul {
width: 100%;
display: none;
}
#cssmenu.small-screen.align-center > ul {
text-align: left;
}
#cssmenu.small-screen ul li {
width: 100%;
border-top: 1px solid rgba(120, 120, 120, 0.2);
}
#cssmenu.small-screen ul ul li,
#cssmenu.small-screen li:hover > ul > li {
height: auto;
}
#cssmenu.small-screen ul li a,
#cssmenu.small-screen ul ul li a {
width: 100%;
border-bottom: 0;
}
#cssmenu.small-screen > ul > li {
float: none;
}
#cssmenu.small-screen ul ul li a {
padding-left: 25px;
}
#cssmenu.small-screen ul ul ul li a {
padding-left: 35px;
}
#cssmenu.small-screen ul ul li a {
color: #dddddd;
background: none;
}
#cssmenu.small-screen ul ul li:hover > a,
#cssmenu.small-screen ul ul li.active > a {
color: #ffffff;
}
#cssmenu.small-screen ul ul,
#cssmenu.small-screen ul ul ul,
#cssmenu.small-screen.align-right ul ul {
position: relative;
left: 0;
width: 100%;
margin: 0;
text-align: left;
}
#cssmenu.small-screen > ul > li.has-sub > a:after,
#cssmenu.small-screen > ul > li.has-sub > a:before,
#cssmenu.small-screen ul ul > li.has-sub > a:after,
#cssmenu.small-screen ul ul > li.has-sub > a:before {
display: none;
}
#cssmenu.small-screen #menu-button {
display: block;
padding: 17px;
color: #dddddd;
cursor: pointer;
font-size: 12px;
text-transform: uppercase;
font-weight: 700;
}
#cssmenu.small-screen #menu-button:after {
position: absolute;
top: 22px;
right: 17px;
display: block;
height: 4px;
width: 20px;
border-top: 2px solid #dddddd;
border-bottom: 2px solid #dddddd;
content: '';
box-sizing: content-box;
}
#cssmenu.small-screen #menu-button:before {
position: absolute;
top: 16px;
right: 17px;
display: block;
height: 2px;
width: 20px;
background: #dddddd;
content: '';
box-sizing: content-box;
}
#cssmenu.small-screen #menu-button.menu-opened:after {
top: 23px;
border: 0;
height: 2px;
width: 15px;
background: #ffffff;
-webkit-transform: rotate(45deg);
-moz-transform: rotate(45deg);
-ms-transform: rotate(45deg);
-o-transform: rotate(45deg);
transform: rotate(45deg);
}
#cssmenu.small-screen #menu-button.menu-opened:before {
top: 23px;
background: #ffffff;
width: 15px;
-webkit-transform: rotate(-45deg);
-moz-transform: rotate(-45deg);
-ms-transform: rotate(-45deg);
-o-transform: rotate(-45deg);
transform: rotate(-45deg);
}
#cssmenu.small-screen .submenu-button {
position: absolute;
z-index: 99;
right: 0;
top: 0;
display: block;
border-left: 1px solid rgba(120, 120, 120, 0.2);
height: 46px;
width: 46px;
cursor: pointer;
}
#cssmenu.small-screen .submenu-button.submenu-opened {
background: #6269cd;
}
#cssmenu.small-screen ul ul .submenu-button {
height: 34px;
width: 34px;
}
#cssmenu.small-screen .submenu-button:after {
position: absolute;
top: 22px;
right: 19px;
width: 8px;
height: 2px;
display: block;
background: #dddddd;
content: '';
}
#cssmenu.small-screen ul ul .submenu-button:after {
top: 15px;
right: 13px;
}
#cssmenu.small-screen .submenu-button.submenu-opened:after {
background: #ffffff;
}
#cssmenu.small-screen .submenu-button:before {
position: absolute;
top: 19px;
right: 22px;
display: block;
width: 2px;
height: 8px;
background: #dddddd;
content: '';
}
#cssmenu.small-screen ul ul .submenu-button:before {
top: 12px;
right: 16px;
}
#cssmenu.small-screen .submenu-button.submenu-opened:before {
display: none;
}
#cssmenu.small-screen.select-list {
padding: 5px;
}
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<!-- jQuery -->
<script src="http://code.jquery.com/jquery-latest.min.js"></script>
<!-- MenuMaker Plugin -->
<script src="https://s3.amazonaws.com/menumaker/menumaker.min.js"></script>
<!-- Icon Library -->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/font-awesome/4.5.0/css/font-awesome.min.css">
<title>Test</title>
</head>
<body>
<div id="cssmenu">
<ul>
<li><i class="fa fa-fw fa-home"></i> Home</li>
<li><i class="fa fa-fw fa-bars"></i> Menus
<ul>
<li>Sub menu 1
<ul>
<li>Child menu 1</li>
<li>Child menu 2</li>
</ul>
</li>
<li>Sub menu 2
<ul>
<li>Child menu 1</li>
<li>Child menu 2
<ul>
<li>Grand menu</li>
</ul>
</li>
</ul>
</li>
<li>Sub menu 3</li>
</ul>
</li>
<li><i class="fa fa-fw fa-cog"></i> Settings</li>
<li><i class="fa fa-fw fa-phone"></i> Contact</li>
</ul>
</div>
</body>
</html>