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

body {
    font-family: 'Inter', sans-serif;
    background: #f8f9fb;
    color: #222;
    line-height: 1.8;
}

header {
    padding: 60px 20px;
    text-align: center;
    background: linear-gradient(135deg,#0f2027,#203a43,#2c5364);
    color: white;
}

header h1 {
    font-size: 32px;
    max-width: 900px;
    margin: auto;
}

.subtitle {
    font-weight: 300;
    margin-top: 10px;
}

.author {
    margin-top: 15px;
    font-size: 14px;
    opacity: 0.8;
}

nav {
    background: white;
    position: sticky;
    top: 0;
    z-index: 1000;
    box-shadow: 0 2px 8px rgba(0,0,0,0.05);
}

nav ul {
    display: flex;
    justify-content: center;
    list-style: none;
}

nav li {
    margin: 15px;
}

nav a {
    text-decoration: none;
    color: #333;
    font-weight: 500;
}

main {
    max-width: 900px;
    margin: auto;
    padding: 50px 20px;
}

section {
    margin-bottom: 80px;
}

h2 {
    margin-bottom: 20px;
    border-left: 4px solid #2c5364;
    padding-left: 10px;
}

.figure {
    margin: 40px 0;
    text-align: center;
}

.figure img {
    width: 100%;
    border-radius: 8px;
    box-shadow: 0 10px 25px rgba(0,0,0,0.1);
}

.figure p {
    font-size: 14px;
    margin-top: 10px;
    color: #555;
}

.equation {
    background: #eef2f7;
    padding: 15px;
    margin: 20px 0;
    font-family: monospace;
    text-align: center;
    border-radius: 6px;
}

.highlight-box {
    background: #203a43;
    color: white;
    padding: 20px;
    border-radius: 8px;
    font-weight: bold;
    margin: 30px 0;
    text-align: center;
}

footer {
    text-align: center;
    padding: 30px;
    background: #111;
    color: white;
}

#progress-bar {
    height: 5px;
    width: 0%;
    background: #2c5364;
    position: fixed;
    top: 0;
    left: 0;
    z-index: 2000;
}

@media(max-width:768px){
    header h1 {
        font-size: 22px;
    }
    nav ul {
        flex-wrap: wrap;
    }
}