component dropdown

Компонентная вёрстка

CSS-компонент "Dropdown menu"

html

<nav id="nav">
    <ul class="main-nav">
        <li>
            <a href="#">Main-item 01</a>
	    <ul class="dropdown">
	        <li><a href="#">Sub-item 01</a></li>
		<li><a href="#">Sub-item 02</a></li>
		<li><a href="#">Sub-item 03</a></li>
		<li><a href="#">Sub-item 04</a></li>
            </ul>
        </li>
        <li><a href="#">Main-item 02</a></li>
        <li><a href="#">Main-item 03</a></li>
        <li><a href="#">Main-item 04</a></li>
    </ul>
</nav>

css

:root {
    --hover-back: #457;
    --menu-back: #bbc;
}
html {
    font-family: Arial;
    font-size: 16px;
}
.main-nav {
    font-size: 0;
    line-height: 0;
    background: var(--menu-back);
    padding-left:0;
}

.main-nav > li {
    position: relative;
    display: inline-block;
    vertical-align: top;
    font-size: 1rem;
    line-height: 1rem;
    border-left: 2px solid #fff;
}

.main-nav > li:hover .dropdown {
    opacity: 1;
    visibility: visible;
}

.main-nav > li:hover > a {
    color: #fff;
    background: var(--hover-back);
}

.main-nav > li > a {
    display: block;
    color: var(--hover-back);
    padding: 20px 30px;
    transition: background .5s ease;
    text-decoration: none;
}

.main-nav a:hover {
    color: #fff;
    background: var(--hover-back);
}

.dropdown {
    position: absolute;
    z-index: 10;
    left: 0;
    top: 100%;
    width: 100%;
    background: #dde;
    border: 2px solid #fff;
    opacity: 0;
    visibility: hidden;
    transition: opacity .5s ease;
    padding-left: 0;
}

.dropdown > li {
    border-bottom: 1px solid #fff;
    list-style-type: none; 
    list-style-position: outside;
}

.dropdown > li:last-child {
    border-bottom: 0;
}

.dropdown > li > a {
    display: block;
    padding: 1rem;
    text-decoration: none;
    color: #555;
}