<div id="wrap">

	<div id="side">
		<div id="menu">
			<div class="m-item">
				<div class="m-item__link">
					<a href="#">Link</a>
					<span></span>
				</div>
				<div class="m-item__drop">
					<div class="m-grid">

						<div class="m-frame">
							<div class="m-frame__title"><span>Title</span></div>
							<div class="m-frame__list">
								<div class="m-frame-link">
									<div class="m-frame-link__name">Item</div>
									<div class="m-frame-link__val">42</div>
								</div>
								<div class="m-frame-link">
									<div class="m-frame-link__name">Item</div>
									<div class="m-frame-link__val">42</div>
								</div>
								<div class="m-frame-link">
									<div class="m-frame-link__name">Item</div>
									<div class="m-frame-link__val">42</div>
								</div>
								<div class="m-frame-link">
									<div class="m-frame-link__name">Item</div>
									<div class="m-frame-link__val">42</div>
								</div>
							</div>
						</div>

						<div class="m-frame">
							<div class="m-frame__title"><span>Title</span></div>
							<div class="m-frame__list">
								<div class="m-frame-link">
									<div class="m-frame-link__name">Item</div>
									<div class="m-frame-link__val">42</div>
								</div>
								<div class="m-frame-link">
									<div class="m-frame-link__name">Item</div>
									<div class="m-frame-link__val">42</div>
								</div>
								<div class="m-frame-link">
									<div class="m-frame-link__name">Item</div>
									<div class="m-frame-link__val">42</div>
								</div>
								<div class="m-frame-link">
									<div class="m-frame-link__name">Item</div>
									<div class="m-frame-link__val">42</div>
								</div>
							</div>
						</div>

						<div class="m-frame">
							<div class="m-frame__title"><span>Title</span></div>
							<div class="m-frame__list">
								<div class="m-frame-link">
									<div class="m-frame-link__name">Item</div>
									<div class="m-frame-link__val">42</div>
								</div>
								<div class="m-frame-link">
									<div class="m-frame-link__name">Item</div>
									<div class="m-frame-link__val">42</div>
								</div>
								<div class="m-frame-link">
									<div class="m-frame-link__name">Item</div>
									<div class="m-frame-link__val">42</div>
								</div>
								<div class="m-frame-link">
									<div class="m-frame-link__name">Item</div>
									<div class="m-frame-link__val">42</div>
								</div>
							</div>
						</div>

					</div>
				</div>
			</div>

			<div class="m-item">
				<div class="m-item__link">
					<a href="#">Link with a very very very long name</a>
					<span></span>
				</div>
				<div class="m-item__drop">
					<div class="m-grid">

						<div class="m-frame">
							<div class="m-frame__title"><span>Title</span></div>
							<div class="m-frame__list">
								<div class="m-frame-link">
									<div class="m-frame-link__name">Item</div>
									<div class="m-frame-link__val">42</div>
								</div>
								<div class="m-frame-link">
									<div class="m-frame-link__name">Item</div>
									<div class="m-frame-link__val">42</div>
								</div>
								<div class="m-frame-link">
									<div class="m-frame-link__name">Item</div>
									<div class="m-frame-link__val">42</div>
								</div>
								<div class="m-frame-link">
									<div class="m-frame-link__name">Item</div>
									<div class="m-frame-link__val">42</div>
								</div>
							</div>
						</div>

						<div class="m-frame">
							<div class="m-frame__title"><span>Title</span></div>
							<div class="m-frame__list">
								<div class="m-frame-link">
									<div class="m-frame-link__name">Item</div>
									<div class="m-frame-link__val">42</div>
								</div>
								<div class="m-frame-link">
									<div class="m-frame-link__name">Item</div>
									<div class="m-frame-link__val">42</div>
								</div>
								<div class="m-frame-link">
									<div class="m-frame-link__name">Item</div>
									<div class="m-frame-link__val">42</div>
								</div>
								<div class="m-frame-link">
									<div class="m-frame-link__name">Item</div>
									<div class="m-frame-link__val">42</div>
								</div>
							</div>
						</div>

					</div>
				</div>
			</div>
		</div>
	</div>

</div>
// autoprefixer: true

html,
body {
	margin: 0;
	padding: 0;
	font-family: sans-serif;
	font-size: 16px;
	line-height: 1.4;
	color: #555;
	background: #fff;
}

* {
	box-sizing: border-box;
}

#wrap {
	position: relative;
}

.centerer {
	width: 100%;
	padding: 20px;
	max-width: 1200px;
	margin: auto;
}

#side {
	position: fixed;
	z-index: 99;
	top: 0;
	bottom: 0;
	left: 0;
	width: 240px;
	background: #eee;
}

#menu {}

.m-item {
	position: relative;

	&__link {
		display: flex;
		align-items: center;
		justify-content: space-between;
		padding: 10px;

		a {
			text-decoration: none;
			flex-grow: 1;
			text-overflow: ellipsis;
			overflow: hidden;
			white-space: nowrap;
		}

		span {
			flex: 0 0 auto;
			display: block;
			width: 16px;
			height: 16px;
			position: relative;

			&::before {
				content: '';
				display: block;
				position: absolute;
				top: 0;
				right: 0;
				bottom: 0;
				left: 0;
				margin: auto;
				width: 10px;
				height: 10px;
				border-top: 2px solid #000;
				border-right: 2px solid #000;
				transform: rotate(45deg);
			}
		}
	}

	&__drop {
		position: absolute;
		top: 0;
		left: 100%;
		background: #ccc;
		padding: 10px;
		display: none;
	}
	
	&:hover {
		background: fade(#000, 5%);
		
		.m-item {
			&__drop {
				display: block;
			}
		}
	}
}

.m-grid {
	display: grid;
	grid-template-columns: repeat(2, 1fr);
}

.m-frame {
	padding: 10px;

	&__title {
		padding-bottom: 10px;
		margin-bottom: 10px;
		border-bottom: 1px solid #aaa;
		font-weight: 700;
	}

	&__list {
		padding: 10px;
	}

	&-link {
		display: flex;
		margin-bottom: 10px;
		
		&:last-child {
			margin-bottom: 0;
		}

		&__name {
			flex-grow: 1;
		}

		&__val {
			&::before {
				content: '\a0(';
			}

			&::after {
				content: ')';
			}
		}
	}
}

@media (max-width: 600px) {
	.m-item {
		&__drop {
			position: static;
		}
	}
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/jquery/3.4.1/jquery.min.js