JSFiddle - React, Tailwind, and code Playground

HTML

<div class="table">
  <div class="header">
    <div class="header_row">
      <div class="header_cell" style="width: 150px;">Januar</div><!--
      --><div class="header_cell" style="width: 120px;">Februar</div><!--
      --><div class="header_cell" style="width: 120px;">März</div><!--
      --><div class="header_cell" style="width: 150px;">April</div><!--
      --><div class="header_cell" style="width: 120px;">Mai</div><!--
      --><div class="header_cell" style="width: 120px;">Juni</div><!--
      --><div class="header_cell" style="width: 150px;">Juli</div><!--
      --><div class="header_cell" style="width: 120px;">August</div><!--
      --><div class="header_cell" style="width: 120px;">September</div><!--
      --><div class="header_cell" style="width: 150px;">Oktober</div><!--
      --><div class="header_cell" style="width: 120px;">November</div><!--
      --><div class="header_cell" style="width: 150px;">Dezember</div>
    </div>
    <div class="header_row" id="gantt_chart_header_week">    
      <div class="week_column header_cell">1</div><!--
      --><div class="week_column header_cell">2</div><!--
      --><div class="week_column header_cell">3</div><!--
      --><div class="week_column header_cell">4</div><!--
      --><div class="week_column header_cell">5</div><!--
      --><div class="week_column header_cell">6</div><!--
      --><div class="week_column header_cell">7</div><!--
      --><div class="week_column header_cell">8</div><!--
      --><div class="week_column header_cell">9</div><!--
      --><div class="week_column header_cell">11</div><!--
      --><div class="week_column header_cell">10</div><!--
      --><div class="week_column header_cell">12</div><!--
      --><div class="week_column header_cell">13</div><!--
      --><div class="week_column header_cell">14</div><!--
      --><div class="week_column header_cell">15</div><!--
      --><div class="week_column header_cell">16</div><!--
      --><div class="week_column...

CSS

.table
{
  white-space: nowrap;
  overflow-x: auto;
  overflow-y: hidden;
  width: 50%;
}

.header
{
  height: 3em;
  background: -webkit-linear-gradient(#D7D6D6 0%, #959595 100%); 
  background: -moz-linear-gradient(#D7D6D6 0%, #959595 100%); 
  background: -o-linear-gradient(#D7D6D6 0%, #959595 100%); 
  background: linear-gradient(#D7D6D6 0%, #959595 100%);
}

.header.fixed
{
    background-attachment: fixed;
}

.header .header_row
{
    height: 1.5em;
}

.header .header_row .header_cell
{
    display: inline-block;
    outline: 1px solid #000;
    text-align: center;
    height: 1.5em;
}

.header .header_row .week_column
{
    width: 30px;
}