Building the Header Component

Header Component Overview

The header is the first component users see. It contains the logo, search functionality, navigation links, and a shopping cart indicator. We’ll build it using Flexbox for layout and BEM methodology for naming.

Component Structure

<header class="header">
  <div class="header__container">
    <div class="header__logo">...</div>
    <div class="header__search">...</div>
    <nav class="header__nav">...</nav>
  </div>
  <div class="header__categories">...</div>
</header>

Building the HTML

Create the Header Element

Start with a semantic <header> element. Use the header class for styling and an ID for JavaScript access:

<header class="header" id="main-header">
  <div class="header__container">
    <!-- Content goes here -->
  </div>
</header>

BEM Block: header is the main block. All child elements will use header__ prefix.

Add the Logo

Create a clickable logo that links to the homepage:

<div class="header__logo">
  <a href="/" class="header__logo-link">
    <span class="header__logo-text">ML</span>
    <span class="header__logo-subtitle">Store</span>
  </a>
</div>

The logo uses two <span> elements so we can style them differently.

Build the Search Bar

Add a search form with input and button:

<div class="header__search">
  <form class="header__search-form" action="/buscar" method="GET">
    <input 
      type="search" 
      class="header__search-input" 
      placeholder="Buscar productos, marcas y más..." 
      name="q"
      id="search-input"
      autocomplete="off"
    />
    <button type="submit" class="header__search-button" aria-label="Buscar">
      <svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
        <circle cx="11" cy="11" r="8"></circle>
        <path d="m21 21-4.35-4.35"></path>
      </svg>
    </button>
  </form>
</div>

Use type="search" instead of type="text" for better mobile keyboard and browser features.

Create Navigation Links

Add navigation using semantic <nav> and an unordered list:

<nav class="header__nav">
  <ul class="header__nav-list">
    <li class="header__nav-item">
      <a href="#" class="header__nav-link">Crear cuenta</a>
    </li>
    <li class="header__nav-item">
      <a href="#" class="header__nav-link">Ingresar</a>
    </li>
    <li class="header__nav-item">
      <a href="#" class="header__nav-link">Mis compras</a>
    </li>
    <li class="header__nav-item">
      <a href="#" class="header__nav-link header__nav-link--cart" data-cart-count="0">
        <!-- Cart SVG icon -->
        <span class="header__cart-label">Carrito</span>
      </a>
    </li>
  </ul>
</nav>

Notice the cart link has:

A modifier class: header__nav-link--cart
A data attribute: data-cart-count="0" (for the badge)

Add Category Bar

Add a secondary navigation below the main header:

<div class="header__categories">
  <nav class="header__categories-nav">
    <ul class="header__categories-list">
      <li class="header__categories-item">
        <a href="#" class="header__categories-link">Categorías</a>
      </li>
      <li class="header__categories-item">
        <a href="#" class="header__categories-link">Ofertas</a>
      </li>
      <!-- More categories -->
    </ul>
  </nav>
</div>

Styling with CSS

Main Header Block

.header {
  /* Gradient background (Mercado Libre style) */
  background: linear-gradient(
    to bottom, 
    var(--color-primary), 
    var(--color-primary-dark)
  );
  
  /* Sticky positioning: stays at top when scrolling */
  position: sticky;
  top: 0;
  z-index: 100;
  
  /* Subtle shadow for depth */
  box-shadow: var(--shadow-sm);
}

Sticky Positioning: The header behaves normally until you scroll past it, then it “sticks” to the top. The z-index: 100 ensures it stays above other content.

Flexbox Container

.header__container {
  /* Flexbox for horizontal layout */
  display: flex;
  align-items: center;        /* Vertical centering */
  justify-content: space-between; /* Logo left, nav right */
  gap: var(--spacing-md);     /* Space between items */
  
  /* Constrain width and center */
  max-width: var(--container-max-width);
  margin: 0 auto;
  padding: var(--spacing-md) var(--spacing-lg);
}

Flexbox Properties Explained:

display: flex - Activates flexbox layout
align-items: center - Centers children vertically
justify-content: space-between - Pushes first item left, last item right
gap - Adds space between flex items (cleaner than margin)

Logo Styling

.header__logo {
  flex-shrink: 0; /* Don't let the logo shrink */
}

.header__logo-link {
  display: flex;
  align-items: baseline; /* Align text baseline */
  gap: var(--spacing-xs);
  transition: transform var(--transition-fast);
}

.header__logo-link:hover {
  transform: scale(1.02); /* Subtle grow effect */
}

.header__logo-text {
  font-size: var(--font-size-2xl);
  font-weight: 700;
  color: var(--color-secondary);
}

.header__logo-subtitle {
  font-size: var(--font-size-lg);
  font-weight: 400;
  color: var(--color-gray-600);
}

Search Bar Styling

.header__search {
  flex: 1; /* Take all available space */
  max-width: 600px;
}

.header__search-form {
  display: flex;
  border-radius: var(--border-radius-sm);
  overflow: hidden; /* Makes children respect border-radius */
  box-shadow: var(--shadow-sm);
}

.header__search-input {
  flex: 1; /* Input takes remaining space */
  padding: var(--spacing-sm) var(--spacing-md);
  border: none;
  font-size: var(--font-size-base);
  min-width: 0; /* Important for flex items to shrink */
}

.header__search-input::placeholder {
  color: var(--color-gray-400);
}

.header__search-button {
  display: flex;
  align-items: center;
  justify-content: center;
  padding: var(--spacing-sm) var(--spacing-md);
  background-color: var(--color-secondary);
  color: var(--color-white);
  transition: background-color var(--transition-fast);
}

.header__search-button:hover {
  background-color: var(--color-secondary-dark);
}

overflow: hidden on the form makes the input and button respect the parent’s border-radius.

.header__nav {
  flex-shrink: 0; /* Don't shrink navigation */
}

.header__nav-list {
  display: flex;
  align-items: center;
  gap: var(--spacing-md);
}

.header__nav-link {
  display: flex;
  align-items: center;
  gap: var(--spacing-xs);
  padding: var(--spacing-xs) var(--spacing-sm);
  font-size: var(--font-size-sm);
  color: var(--color-gray-600);
  border-radius: var(--border-radius-sm);
  transition: background-color var(--transition-fast);
  white-space: nowrap; /* Prevent text wrapping */
}

.header__nav-link:hover {
  background-color: rgba(0, 0, 0, 0.05);
}

Cart Badge with CSS

.header__nav-link--cart {
  position: relative; /* For absolute positioning of badge */
}

/* Show badge only when count > 0 */
.header__nav-link--cart[data-cart-count]:not([data-cart-count="0"])::after {
  content: attr(data-cart-count); /* Read from data attribute */
  
  /* Position in top-right corner */
  position: absolute;
  top: -4px;
  right: -8px;
  
  /* Badge styling */
  min-width: 18px;
  height: 18px;
  padding: 0 var(--spacing-xs);
  background-color: var(--color-error);
  color: var(--color-white);
  font-size: var(--font-size-xs);
  font-weight: 600;
  border-radius: var(--border-radius-full);
  
  /* Center the number */
  display: flex;
  align-items: center;
  justify-content: center;
}

content: attr(data-cart-count) - This CSS reads the value from the HTML attribute and displays it. When JavaScript updates the attribute, the badge updates automatically!

Category Bar

.header__categories {
  background-color: var(--color-white);
  border-top: 1px solid rgba(0, 0, 0, 0.1);
}

.header__categories-nav {
  max-width: var(--container-max-width);
  margin: 0 auto;
  padding: 0 var(--spacing-lg);
}

.header__categories-list {
  display: flex;
  gap: var(--spacing-lg);
  overflow-x: auto; /* Allow horizontal scroll on mobile */
  -webkit-overflow-scrolling: touch; /* Smooth scroll on iOS */
  
  /* Hide scrollbar */
  scrollbar-width: none; /* Firefox */
  -ms-overflow-style: none; /* IE/Edge */
}

/* Hide scrollbar in Chrome/Safari */
.header__categories-list::-webkit-scrollbar {
  display: none;
}

.header__categories-link {
  display: block;
  padding: var(--spacing-sm) 0;
  font-size: var(--font-size-sm);
  color: var(--color-gray-500);
  white-space: nowrap;
  transition: color var(--transition-fast);
}

.header__categories-link:hover {
  color: var(--color-secondary);
}

Key Concepts Explained

BEM in Action

Notice how all classes follow the BEM pattern:

header                    (Block)
├── header__container     (Element)
├── header__logo          (Element)
│   ├── header__logo-link
│   ├── header__logo-text
│   └── header__logo-subtitle
├── header__search        (Element)
│   ├── header__search-form
│   ├── header__search-input
│   └── header__search-button
└── header__nav           (Element)
    ├── header__nav-list
    ├── header__nav-item
    └── header__nav-link--cart  (Modifier)

Flexbox Layout Strategy

The header uses Flexbox to create a responsive layout:

Logo (flex-shrink: 0) - Never shrinks, maintains size
Search (flex: 1) - Grows to fill available space
Navigation (flex-shrink: 0) - Never shrinks, maintains size

This ensures the search bar is flexible while logo and nav remain constant.

Accessibility Features

Semantic HTML - Using <header>, <nav>, <form> for screen readers

aria-label - Describing the search button icon

Keyboard Navigation - All links and buttons are focusable

Focus Styles - Visible focus indicators (defined in global CSS)

Complete Header Code

See the full implementation:

HTML: /workspace/source/mi-tutorial/index.html:234-415
CSS: /workspace/source/mi-tutorial/src/style.css:452-832

Next Steps

Hero Section

Build an eye-catching hero banner with gradients

Shopping Cart

Learn how to update the cart badge dynamically

Get Started

HTML Fundamentals

CSS Fundamentals

TypeScript Basics

Project Tutorial

Header Component Overview

Component Structure

Building the HTML

Styling with CSS

Main Header Block

Flexbox Container

Logo Styling

Search Bar Styling

Navigation Styling

Cart Badge with CSS

Category Bar

Key Concepts Explained

BEM in Action

Flexbox Layout Strategy

Accessibility Features

Complete Header Code

Next Steps

Hero Section

Shopping Cart

Build docs developers (and LLMs) love

Get Started

HTML Fundamentals

CSS Fundamentals

TypeScript Basics

Project Tutorial

Documentation Index

​Header Component Overview

​Component Structure

​Building the HTML

​Styling with CSS

​Main Header Block

​Flexbox Container

​Logo Styling

​Search Bar Styling

​Navigation Styling

​Cart Badge with CSS

​Category Bar

​Key Concepts Explained

​BEM in Action

​Flexbox Layout Strategy

​Accessibility Features

​Complete Header Code

​Next Steps

Hero Section

Shopping Cart

Build docs developers (and LLMs) love

Header Component Overview

Component Structure

Building the HTML

Styling with CSS

Main Header Block

Flexbox Container

Logo Styling

Search Bar Styling

Navigation Styling

Cart Badge with CSS

Category Bar

Key Concepts Explained

BEM in Action

Flexbox Layout Strategy

Accessibility Features

Complete Header Code

Next Steps