Result

CSS Gridを使ったガントチャートの実装例です

css

body,
html {
  background-color: #cddade;
  height: 100%;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}


.wrapper {
  max-width: 1200px;
  min-width: 700px;
  margin: 0 auto;
  padding: 40px;
}

.gantt {
  display: grid;
  border: 0;
  border-radius: 12px;
  position: relative;
  overflow: hidden;
  box-sizing: border-box;
 
}
.gantt__row {
  display: grid;
  grid-template-columns: 150px 1fr;
  background-color: #fff;
}
.gantt__row:nth-child(odd) {
  background-color: #f5f5f5;
}
.gantt__row:nth-child(odd) .gantt__row-first {
  background-color: #f5f5f5;
}
.gantt__row:nth-child(3) .gantt__row-bars {
  border-top: 0;
}
.gantt__row:nth-child(3) .gantt__row-first {
  border-top: 0;
}
.gantt__row--empty {
  background-color: #ffd6d2 !important;
  z-index: 1;
}
.gantt__row--empty .gantt__row-first {
  border-width: 1px 1px 0 0;
}
.gantt__row--lines {
  position: absolute;
  height: 100%;
  width: 100%;
  background-color: transparent;
  grid-template-columns: 150px repeat(12, 1fr);
}
.gantt__row--lines span {
  display: block;
  border-right: 1px solid rgba(0, 0, 0, 0.1);
}
.gantt__row--lines span.marker {
  background-color: rgba(10, 52, 68, 0.13);
  z-index: 2;
}
.gantt__row--lines:after {
  grid-row: 1;
  grid-column: 0;
  background-color: #1688b345;
  z-index: 2;
  height: 100%;
}
.gantt__row--months {
  color: #fff;
  background-color: #0a3444 !important;
  border-bottom: 1px solid rgba(0, 0, 0, 0.1);
  grid-template-columns: 150px repeat(12, 1fr);
}
.gantt__row--months .gantt__row-first {
  border-top: 0 !important;
  background-color: #0a3444 !important;
}
.gantt__row--months span {
  text-align: center;
  font-size: 13px;
  align-self: center;
  font-weight: bold;
  padding: 20px 0;
}
.gantt__row-first {
  background-color: #fff;
  border-width: 1px 0 0 0;
  border-color: rgba(0, 0, 0, 0.1);
  border-style: solid;
  padding: 15px 0;
  font-size: 13px;
  font-weight: bold;
  text-align: center;
}
.gantt__row-bars {
  list-style: none;
  display: grid;
  padding: 9px 0;
  margin: 0;
  grid-template-columns: repeat(12, 1fr);
  grid-gap: 8px 0;
  border-top: 1px solid rgba(221, 221, 221, 0.8);
}
.gantt__row-bars li {
  text-align: left;
  min-height: 15px;
  background-color: #55de84;
  padding: 5px 12px;
  color: #fff;
  overflow: hidden;
  position: relative;
  cursor: pointer;
  border-radius: 20px;
}

.gantt__row-bars li:before, .gantt__row-bars li:after {
  content: "";
  height: 100%;
  top: 0;
  z-index: 4;
  position: absolute;
  background-color: rgba(0, 0, 0, 0.3);
}
.gantt__row-bars li:before {
  left: 0;
}
.gantt__row-bars li:after {
  right: 0;
}

html

<div class="wrapper">
	<div class="gantt">
		<div class="gantt__row gantt__row--months">
			<div class="gantt__row-first"></div>
			<span>1月</span><span>2月</span><span>3月</span>
			<span>4月</span><span>5月</span><span>6月</span>
			<span>7月</span><span>8月</span><span>9月</span>
			<span>10月</span><span>11月</span>
			<span>12月</span>
		</div>
		<div class="gantt__row gantt__row--lines" data-month="5">
			<span></span><span></span><span></span>
			<span></span><span></span><span></span>
			<span></span><span class="marker"></span><span></span>
			<span></span><span></span><span></span>
		</div>
		<div class="gantt__row">
			<div class="gantt__row-first">
				佐藤
			</div>
			<ul class="gantt__row-bars">
				<li style="grid-column: 4/11; background-color: #2ecaac;">ディレクション</li>
			</ul>
		</div>
		<div class="gantt__row gantt__row--empty">
　　　・
　　　・
　　　・

チャートはマークアップで管理しています。
grid-column: 4/11;等とすれば4～11月まで設定できる仕組み。

via

CSS-Grid Gantt Chart