JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Document</title>
</head>
<body>
  <div class="main-block">
    <div class="sidebar">
      <div class="sidebar-content">
        <p>sometext for example for stackoverfrom</p>
        <p>sometext for example for stackoverfrom</p>
        <p>sometext for example for stackoverfrom</p>
        <p>sometext for example for stackoverfrom</p>
        <p>sometext for example for stackoverfrom</p>
        <p>sometext for example for stackoverfrom</p>
        <p>last string</p>
      </div>
    </div>
    <div class="main-content">
      
    </div>
  </div>
</body>
</html>

CSS

.main-block  {
   display: flex;
}

.sidebar {
  background-color: LightCoral;
  width: 25%;
}

.sidebar-content {
  margin: 5px;
  margin-bottom: 40px;
  background-color: LimeGreen;
  position: sticky;
  top: 0;
}

.main-content {
  width: 75%;
  height: 4000px;
  background-color: LightBlue;
}