**HTML (`index.html`)**:
```html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<link rel="stylesheet" href="styles.css">
<title>Weather</title>
</head>
<body>
<nav>
<a href="index.html">Home</a>
<a href="about.html">About</a>
<a href="cities.html">Cities</a>
</nav>
<div class="weather-container">
<h1>Weather in Your City</h1>
<input type="text" id="city-input" placeholder="Enter city">
<button id="check-weather">Check Weather</button>
<div class="weather-info">
<h2 id="city-name"></h2>
<p id="temperature"></p>
<p id="description"></p>
</div>
</div>
<script src="script.js"></script>
</body>
</html>
```
**HTML (`about.html`)**:
```html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<link rel="stylesheet" href="styles.css">
<title>About</title>
</head>
<body>
<nav>
<a href="index.html">Home</a>
<a href="about.html">About</a>
<a href="cities.html">Cities</a>
</nav>
<div class="content">
<h1>About this Weather App</h1>
<p>This app provides weather information for cities around the world. Built with HTML, CSS, and JavaScript.</p>
</div>
</body>
</html>
```
**HTML (`cities.html`)**:
```html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<link rel="stylesheet" href="styles.css">
<title>Cities</title>
</head>
<body>
<nav>
<a href="index.html">Home</a>
<a href="about.html">About</a>
<a href="cities.html">Cities</a>
</nav>
<div class="content">
<h1>Weather in Bulgarian Cities</h1>
<div class="city-weather">
<h2>Sofia</h2>
<p>Temperature: 20°C</p>
<p>Condition: Sunny</p>
</div>
<div class="city-weather">
<h2>Plovdiv</h2>
<p>Temperature: 22°C</p>
<p>Condition: Partly Cloudy</p>
</div>
<div class="city-weather">
<h2>Varna</h2>
<p>Temperature: 19°C</p>
<p>Condition: Rainy</p>
</div>
</div>
</body>
</html>
```
**CSS (`styles.css`)**:
```css
body {
font-family: Arial, sans-serif;
background-color: #e9f7fa;
padding: 20px;
}
nav {
display: flex;
justify-content: space-between;
padding: 10px;
background-color: #4CAF50;
}
nav a {
color: white;
text-decoration: none;
margin: 0 10px;
}
nav a:hover {
text-decoration: underline;
}
.weather-container {
box-shadow: 0px 0px 10px rgba(0, 0, 0, 0.1);
padding: 20px;
background-color: #ffffff;
border-radius: 10px;
text-align: center;
}
.weather-info {
margin-top: 20px;
}
button {
margin-top: 10px;
padding: 10px 15px;
border: none;
background-color: #4CAF50;
color: white;
cursor: pointer;
border-radius: 5px;
}
button:hover {
background-color: #45a049;
}
.city-weather {
border: 1px solid #e0e0e0;
padding: 10px;
margin-top: 10px;
border-radius: 5px;
}
```