Slide in border from left to right, when hovering UL menu - html

Question

I want this border to slide in from left to right(dropmenus only). But can't figure it out
This is how I got so far, I don't have any ideas no more.
Menu is built with ul and li-s.
Is this possible?
Thanks,
.toggle,
[id^=drop] {
display: none;
}
.toggle_menu,
[id^=drop] {
display: none;
}
nav:after {
content:"";
display:table;
clear:both;
}
nav ul {
padding:0;
margin:0;
list-style: none;
position: relative;
}
nav ul li.active_link a{
font-size:14px;
text-decoration:none;
font-family: 'Lato';
font-weight:600;
}
nav ul li {
margin: 0px;
display:inline-block;
float: left;
background-color: white;
}
nav a {
display:block;
padding: 14px 16px;
color:#FFF;
font-size:14px;
text-decoration:none;
color:black;
font-family: 'Lato';
font-weight:400;
}
nav ul li ul li:hover { /*background: #000000; */}
nav a:hover {
/*background-color: #000000;*/
}
nav ul li ul{
display: none;
position: absolute;
color: #31302B;
background: #FFF;
cursor: pointer;
box-shadow: inset 0 0 0 0 #b6945d;
-webkit-transition: all ease 1s;
-moz-transition: all ease 1s;
transition: all ease 1s;
}
nav ul li:hover > ul{
box-shadow: inset 900px 0px 0px #b6945d;
color: #fff;
}
nav ul li:hover > ul {
display:inherit;
}
nav ul ul li {
background-color: transparent;
width: auto;
float: left;
display: list-item;
position: relative;
}
nav ul ul ul li {
position: relative;
top:-60px;
left:170px;
}
nav ul li ul li a{
font-style: italic;
background-color: white;
margin-top: 1px;
}
nav ul li ul li a:hover{
font-style:italic;
color:#b6945d;
}
/*li > a:after { content: ' +'; }*/
li > a:only-child:after { content: ''; }
<nav>
<label for="drop" class="toggle_menu"><img src="assets/images/mobile_button.png"></label>
<input type="checkbox" id="drop" />
<ul class="menu">
<li class="active_link">
Avaleht
</li>
<li>
<label for="drop-1" class="toggle">Kunstnik</label>Kunstnik
<input type="checkbox" id="drop-1"/>
<ul>
<li>Kunstnikust</li>
<li>Tööde arhiiv</li>
</ul>
</li>
<li>
<label for="drop-2" class="toggle">E-pood</label>E-pood
<input type="checkbox" id="drop-2"/>
<ul>
<li>Kõik tooted</li>
<li>Seeriatooted</li>
</ul>
</li>
</ul>
</nav>

Answer 1

I have added 10 line css below: Are you looking for this:
.toggle,
[id^=drop] {
display: none;
}
.toggle_menu,
[id^=drop] {
display: none;
}
nav:after {
content:"";
display:table;
clear:both;
}
nav ul {
padding:0;
margin:0;
list-style: none;
position: relative;
}
nav ul li.active_link a{
font-size:14px;
text-decoration:none;
font-family: 'Lato';
font-weight:600;
}
nav ul li {
margin: 0px;
display:inline-block;
float: left;
background-color: white;
}
nav a {
display:block;
padding: 14px 16px;
color:#FFF;
font-size:14px;
text-decoration:none;
color:black;
font-family: 'Lato';
font-weight:400;
}
nav ul li ul li:hover { /*background: #000000; */}
nav a:hover {
/*background-color: #000000;*/
}
nav ul li ul{
display: none;
position: absolute;
color: #31302B;
background: #FFF;
cursor: pointer;
box-shadow: inset 0 0 0 0 #b6945d;
-webkit-transition: all ease 1s;
-moz-transition: all ease 1s;
transition: all ease 1s;
}
nav ul li:hover > ul{
box-shadow: inset 900px 0px 0px #b6945d;
color: #fff;
}
nav ul li:hover > ul {
display:inherit;
}
nav ul ul li {
background-color: transparent;
width: auto;
float: left;
display: list-item;
position: relative;
}
nav ul ul ul li {
position: relative;
top:-60px;
left:170px;
}
nav ul li ul li a{
font-style: italic;
background-color: white;
margin-top: 1px;
}
nav ul li ul li a:hover{
font-style:italic;
color:#b6945d;
}
/*li > a:after { content: ' +'; }*/
li > a:only-child:after { content: ''; }
/**New css for transition**/
nav ul li ul:after {
content: '';
display: block;
border-bottom: 4px solid red;
width: 0;
position: absolute;
left: 0;
-webkit-transition: 1s ease;
transition: 1s ease;
}
nav ul li ul:hover:after {
width: 100%;
}
<nav>
<label for="drop" class="toggle_menu"><img src="assets/images/mobile_button.png"></label>
<input type="checkbox" id="drop" />
<ul class="menu">
<li class="active_link">
Avaleht
</li>
<li>
<label for="drop-1" class="toggle">Kunstnik</label>Kunstnik
<input type="checkbox" id="drop-1"/>
<ul>
<li>Kunstnikust</li>
<li>Tööde arhiiv</li>
</ul>
</li>
<li>
<label for="drop-2" class="toggle">E-pood</label>E-pood
<input type="checkbox" id="drop-2"/>
<ul>
<li>Kõik tooted</li>
<li>Seeriatooted</li>
</ul>
</li>
</ul>
</nav>

Answer 2

Now it works.
.menu {
width: 100%;
height: auto;
background: white;
transition: all 0.3s ease;
}
.menu ul {
padding: 0px;
margin: 0px;
list-style: none;
position: relative;
display: inline-block;
width:100%;
}
.menu > li > ul.sub_menu {
min-width: 10em;
padding: 4px 0;
background-color: #f4f4f4;
border: 1px solid #fff;
}
.menu ul li { padding: 0px; }
.menu ul li.active a{
font-weight:600;
}
.second_menu ul li.active a{
font-weight:600;
}
.menu > ul > li { display: inline-block; }
.menu ul li a {
display: block;
text-decoration: none;
color: black;
font-family: 'Lato';
font-weight:400;
font-size:14px;
}
.menu ul li a:hover {
color: black;
}
.menu ul li.hover > a {
color: black;
}
.menu ul li > a { padding: 15px; }
.menu ul ul {
visibility: hidden;
position: absolute;
top: 100%;
width:auto;
background: white;
}
.menu ul li.active_drop a{
font-weight:600 !important;
color:#b6945d;
}
.menu ul li ul.dropdown_nav li a{
font-weight:400;
}
.menu ul li.active_drop a:hover{
color:#b6945d;
}
.menu ul li:hover > ul {
visibility: visible;
}
.menu ul ul > li {
position: relative;
display: inline;
float: left;
width: auto;
}
.menu ul ul > li a {
padding: 10px 15px;
height: auto;
background: white;
font-style:italic;
}
.menu ul ul > li a:hover {
color: black;
}
.menu ul ul ul {
position: absolute;
left: 100%;
top: 0;
}
/* animating the golden border */
.dropdown_nav {
position: relative;
overflow: hidden;
}
.dropdown_nav:before {
position: absolute;
display: block;
top: 0;
left: 0;
width: 100%;
height: 1px;
content: "";
background-color: #b6945d;
z-index: 1;
transition: transform .5s ease-out;
transform: translateX(-100%);
}
.menu>ul>li:hover .dropdown_nav:before {
transform: translateX(0);
}
<nav id="menu" class="menu">
<ul class="dropdown">
<li>leht</li>
<li class="active">
leht1
<ul class="dropdown_nav">
<li class="dropdown_first active_drop">
leht1.1</li>
<li class="dropdown_last">leht1.2</li>
</ul>
</li>
<li>
leht2
<ul class="dropdown_nav">
<li class="dropdown_first">leht2.1</li>
<li>leht2.2</li>
</ul>
</li>
<li>leht3</li>
<li>leht4</li>
</ul>
</nav>