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

body {
    font-family: 'Segoe UI', Arial, sans-serif;
    line-height: 1.6;
    color: #333;
    background-color: #f4f4f4;
}

header {
    background-color: #1a237e;
    color: #fff;
    padding: 1rem 0;
    border-bottom: 2px solid #3949ab;
}

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

.logo a {
    color: #fff;
    text-decoration: none;
    font-weight: bold;
    font-size: 1.2rem;
}

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

nav ul li {
    margin: 0 1rem;
}

nav ul li a {
    color: #fff;
    text-decoration: none;
    font-weight: bold;
    border: 1px solid transparent;
    padding: 0.3rem 0.6rem;
}

nav ul li a:hover {
    border-color: #fff;
}

nav ul li a.active {
    border: 1px solid #fff;
}

.hero {
    text-align: center;
    padding: 3rem 1rem;
    background: linear-gradient(135deg, #1a237e, #3949ab);
    color: #fff;
}

.hero h1 {
    font-size: 2rem;
    margin-bottom: 0.5rem;
}

.hero p {
    font-size: 1.1rem;
}

main {
    max-width: 1200px;
    margin: 2rem auto;
    padding: 0 1rem;
}

.section {
    background: #fff;
    padding: 1.5rem;
    margin-bottom: 1.5rem;
    border: 1px solid #ddd;
}

.content h2 {
    color: #1a237e;
    margin-bottom: 1rem;
    border-bottom: 1px solid #3949ab;
    padding-bottom: 0.3rem;
}

.content h3 {
    color: #3949ab;
    margin: 1rem 0 0.5rem;
}

.formula {
    font-family: 'Courier New', monospace;
    font-size: 1.3rem;
    text-align: center;
    padding: 1rem;
    background: #e8eaf6;
    border: 1px dashed #1a237e;
    margin: 1rem 0;
}

.references {
    font-size: 0.9rem;
}

.references li {
    margin-bottom: 0.3rem;
}

.calculator {
    background: #fff;
    padding: 1.5rem;
    margin-bottom: 1.5rem;
    border: 1px solid #ddd;
}

.calculator h2 {
    color: #1a237e;
    margin-bottom: 1rem;
    border-bottom: 1px solid #3949ab;
    padding-bottom: 0.3rem;
}

.calculator label {
    display: block;
    margin-bottom: 0.8rem;
}

.calculator input,
.calculator textarea {
    margin-left: 0.5rem;
    padding: 0.3rem;
    border: 1px solid #ccc;
    width: 200px;
}

.calculator button {
    background-color: #1a237e;
    color: #fff;
    border: none;
    padding: 0.6rem 1.2rem;
    cursor: pointer;
}

.calculator button:hover {
    background-color: #3949ab;
}

.chart-section {
    background: #fff;
    padding: 1.5rem;
    border: 1px solid #ddd;
}

.chart-section canvas {
    max-width: 100%;
}

footer {
    text-align: center;
    padding: 1rem;
    background-color: #1a237e;
    color: #fff;
    margin-top: 2rem;
}

@media (max-width: 768px) {
    nav ul {
        flex-direction: column;
        align-items: center;
    }
    nav ul li {
        margin: 0.5rem 0;
    }
    .hero h1 {
        font-size: 1.5rem;
    }
}

/* Tour overlay */
.tour-overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(26, 35, 126, 0.8);
    z-index: 9999;
    display: flex;
    justify-content: center;
    align-items: center;
}

.tour-overlay.hidden {
    display: none;
}

.tour-popup {
    background: #fff;
    border: 1px solid #3949ab;
    padding: 1.5rem;
    max-width: 450px;
    width: 90%;
    font-family: 'Segoe UI', Arial, sans-serif;
}

.tour-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 1rem;
}

.tour-step {
    font-weight: bold;
    color: #1a237e;
}

.tour-skip {
    background: none;
    border: none;
    color: #666;
    cursor: pointer;
    font-size: 0.9rem;
}

.tour-skip:hover {
    color: #333;
}

.tour-content h3 {
    color: #1a237e;
    margin-bottom: 0.5rem;
}

.tour-footer-nav {
    display: flex;
    justify-content: space-between;
    margin-top: 1rem;
}

.tour-btn {
    background-color: #1a237e;
    color: #fff;
    border: none;
    padding: 0.5rem 1rem;
    cursor: pointer;
}

.tour-btn:hover {
    background-color: #3949ab;
}

.tour-btn:disabled {
    background-color: #ccc;
    cursor: not-allowed;
}

.tour-progress {
    display: flex;
    justify-content: center;
    gap: 0.5rem;
    margin-top: 1rem;
}

.tour-dot {
    width: 10px;
    height: 10px;
    border: 1px solid #1a237e;
    cursor: pointer;
}

.tour-dot.active {
    background-color: #1a237e;
}