* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    --primary-color: #00A0DC;
    --secondary-color: #004B6E;
    --background-color: #f5f5f5;
    --text-color: #333;
    --chat-bg: #ffffff;
    --message-bg: #f0f0f0;
    --user-message-bg: #e3f2fd;
    --system-message-bg: #f5f5f5;
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    line-height: 1.6;
    color: var(--text-color);
    background-color: var(--background-color);
}

header {
    background-color: white;
    box-shadow: 0 2px 5px rgba(0,0,0,0.1);
    position: fixed;
    width: 100%;
    top: 0;
    z-index: 1000;
}

nav {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem 2rem;
    max-width: 1200px;
    margin: 0 auto;
}

.logo img {
    height: 40px;
}

nav ul {
    display: flex;
    list-style: none;
    gap: 2rem;
}

nav ul li a {
    text-decoration: none;
    color: var(--text-color);
    font-weight: 500;
    transition: color 0.3s ease;
}

nav ul li a:hover {
    color: var(--primary-color);
}

main {
    margin-top: 70px;
    padding: 2rem;
}

.hero {
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    text-align: center;
    padding: 4rem 2rem;
    border-radius: 10px;
    margin-bottom: 2rem;
}

.hero h1 {
    font-size: 2.5rem;
    margin-bottom: 1rem;
}

.chat-section {
    max-width: 1000px;
    margin: 0 auto;
    background: var(--chat-bg);
    border-radius: 10px;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
    overflow: hidden;
}

.chat-container {
    display: flex;
    flex-direction: column;
    height: 600px;
}

.chat-messages {
    flex-grow: 1;
    overflow-y: auto;
    padding: 1rem;
}

.message {
    margin-bottom: 1rem;
    padding: 1rem;
    border-radius: 10px;
    max-width: 80%;
}

.message.user {
    background-color: var(--user-message-bg);
    margin-left: auto;
}

.message.assistant {
    background-color: var(--message-bg);
    margin-right: auto;
}

.message.system {
    background-color: var(--system-message-bg);
    margin: 0 auto;
    text-align: center;
    font-style: italic;
}

.chat-input-container {
    display: flex;
    gap: 1rem;
    padding: 1rem;
    background-color: white;
    border-top: 1px solid #eee;
}

textarea {
    flex-grow: 1;
    padding: 0.8rem;
    border: 1px solid #ddd;
    border-radius: 5px;
    resize: none;
    font-family: inherit;
}

button {
    background-color: var(--primary-color);
    color: white;
    border: none;
    border-radius: 5px;
    padding: 0 1.5rem;
    cursor: pointer;
    transition: background-color 0.3s ease;
}

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

.about {
    max-width: 800px;
    margin: 2rem auto;
    padding: 2rem;
    background: white;
    border-radius: 10px;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
}

.about h2 {
    color: var(--primary-color);
    margin-bottom: 1rem;
}

.about ul {
    margin-top: 1rem;
    padding-left: 2rem;
}

footer {
    background-color: var(--secondary-color);
    color: white;
    text-align: center;
    padding: 1rem;
    margin-top: 2rem;
}

@media (max-width: 768px) {
    nav {
        flex-direction: column;
        gap: 1rem;
    }

    nav ul {
        flex-direction: column;
        align-items: center;
        gap: 1rem;
    }

    .hero h1 {
        font-size: 2rem;
    }

    .chat-container {
        height: 500px;
    }
}