Creating a T-tab effect in HTML requires a combination of HTML structure and CSS styling. A simple and effective way to create this is by using nested <div> elements with appropriate classes for styling. You can create a parent <div> that holds two child <div>s—one for the vertical part of the T and another for the horizontal part. Using CSS, you can position these elements using properties like position, top, left, width, and height to achieve the desired layout. For example:

    
    .tab {
      position: relative;
      width: 100px; /* Width of the horizontal part */
      height: 20px; /* Height of the horizontal part */
      background-color: #ccc;
    }
    
    .tab:before {
      content: '';
      position: absolute;
      top: 0;
      left: 40px; /* Adjust for centering */
      width: 20px; /* Width of the vertical part */
      height: 100px; /* Height of the vertical part */
      background-color: #ccc;
    }
    
    

This CSS will create a basic T-tab shape. You can adjust the dimensions and colors as per your design requirements. If you want to improve accessibility and include content, consider adding <span> or text inside the parent <div>, ensuring it doesn’t interfere with the layout. Additional functionality can be achieved with flexbox or grid layouts if you require a more complex interface for your web project. Always test your design across different browsers to ensure consistency in appearance.