/* --- CSS Variables for Dark/Light Mode --- */
:root {
    --bg-color: #f5f5f5;
    --text-color: #333;
    --container-bg: white;
    --nav-bg: rgba(255, 255, 255, 0.8);
    --nav-border: #e6e6e6;
    --nav-shadow: rgba(0, 0, 0, 0.08);
    --nav-text: #2c3e50;
    --nav-hover-bg: #eef5fb;
    --nav-hover-text: #2980b9;
    --nav-active-bg: #3498db;
    --nav-active-text: #2980b9;
    --heading-color: #2c3e50;
    --subheading-color: #34495e;
    --border-color: #3498db;
}

[data-theme="dark"] {
    --bg-color: #1a1a1a;
    --text-color: #e0e0e0;
    --container-bg: #2d2d2d;
    --nav-bg: rgba(45, 45, 45, 0.8);
    --nav-border: #404040;
    --nav-shadow: rgba(0, 0, 0, 0.3);
    --nav-text: #e0e0e0;
    --nav-hover-bg: #404040;
    --nav-hover-text: #2980b9;
    --nav-active-bg: #3498db;
    --nav-active-text: #2980b9;
    --heading-color: #ffffff;
    --subheading-color: #e0e0e0;
    --border-color: #3498db;
}

/* --- Dark Mode Toggle --- */
.dark-mode-toggle {
    position: fixed;
    top: 16px;
    left: 16px;
    z-index: 1001;
    background: var(--nav-bg);
    border: 1px solid var(--nav-border);
    border-radius: 50%;
    width: 40px;
    height: 40px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    transition: all 0.3s ease;
    box-shadow: 0 8px 24px var(--nav-shadow);
    -webkit-backdrop-filter: saturate(140%) blur(8px);
    backdrop-filter: saturate(140%) blur(8px);
}

.dark-mode-toggle:hover {
    transform: scale(1.05);
    box-shadow: 0 10px 28px var(--nav-shadow);
}

.dark-mode-toggle svg {
    width: 18px;
    height: 18px;
    color: var(--nav-text);
    transition: all 0.3s ease;
}

/* --- Navigation --- */
.nav {
    position: fixed;
    top: 16px;
    left: 50%;
    transform: translateX(-50%);
    z-index: 1000;
    background: var(--nav-bg);
    border: 1px solid var(--nav-border);
    border-radius: 999px;
    box-shadow: 0 8px 24px var(--nav-shadow);
    -webkit-backdrop-filter: saturate(140%) blur(8px);
    backdrop-filter: saturate(140%) blur(8px);
    height: 40px;
    display: flex;
    align-items: center;
}

.nav-inner {
    display: flex;
    align-items: center;
    gap: 20px;
    padding: 0 16px;
    height: 100%;
}

.nav-links {
    list-style: none;
    display: flex;
    gap: 16px;
    margin: 0;
    padding: 0 4px;
}

.nav-links a {
    display: block;
    padding: 8px 12px;
    text-decoration: none;
    color: var(--nav-text);
    font-size: 14px;
    font-weight: 500;
    transition: color 200ms ease;
    line-height: 1.2;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    text-rendering: optimizeLegibility;
}

.nav-links a:hover,
.nav-links a:focus-visible {
    color: var(--nav-hover-text);
    outline: none;
}

.nav-links a.active {
    color: var(--nav-active-text);
    font-weight: 500;
}

.nav-spacer {
    flex: 1;
}

.hamburger {
    display: none;
    background: var(--nav-bg);
    border: 1px solid var(--nav-border);
    border-radius: 50%;
    width: 40px;
    height: 40px;
    padding: 0;
    cursor: pointer;
    color: var(--nav-text);
    align-items: center;
    justify-content: center;
    transition: all 0.3s ease;
    box-shadow: 0 8px 24px var(--nav-shadow);
    -webkit-backdrop-filter: saturate(140%) blur(8px);
    backdrop-filter: saturate(140%) blur(8px);
}

.hamburger:hover {
    transform: scale(1.05);
    box-shadow: 0 10px 28px var(--nav-shadow);
}

.hamburger:focus-visible {
    outline: 2px solid var(--nav-active-bg);
    outline-offset: 2px;
}

.hamburger svg {
    width: 18px;
    height: 18px;
}

body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 100px 20px 50px;
    background-color: var(--bg-color);
    color: var(--text-color);
    line-height: 1.6;
    transition: background-color 0.3s ease, color 0.3s ease;
}

.container {
    max-width: 800px;
    margin: 0 auto;
    background: var(--container-bg);
    padding: 40px;
    border-radius: 12px;
    box-shadow: 0 4px 20px var(--nav-shadow);
    transition: background-color 0.3s ease, box-shadow 0.3s ease;
}

h1 {
    font-size: 2.5rem;
    margin-bottom: 30px;
    color: var(--heading-color);
    text-align: center;
    transition: color 0.3s ease;
}

h2 {
    font-size: 1.8rem;
    margin: 40px 0 20px;
    color: var(--subheading-color);
    border-bottom: 2px solid var(--border-color);
    padding-bottom: 10px;
    transition: color 0.3s ease, border-color 0.3s ease;
}

h3 {
    font-size: 1.3rem;
    margin: 25px 0 10px;
    color: var(--heading-color);
    transition: color 0.3s ease;
}

/* --- Mobile --- */
@media (max-width: 768px) {
    .nav {
        position: fixed;
        top: 16px;
        right: 16px;
        left: auto;
        transform: none;
        width: 40px;
        height: 40px;
        background: var(--nav-bg);
        border: 1px solid var(--nav-border);
        border-radius: 50%;
        box-shadow: 0 8px 24px var(--nav-shadow);
        -webkit-backdrop-filter: saturate(140%) blur(8px);
        backdrop-filter: saturate(140%) blur(8px);
    }

    .nav-inner {
        padding: 0;
        gap: 0;
        display: flex;
        align-items: center;
        justify-content: center;
        height: 100%;
        width: 100%;
    }

    .nav-links {
        display: none;
        position: absolute;
        top: 52px;
        right: 0;
        background: var(--nav-bg);
        border: 1px solid var(--nav-border);
        border-radius: 12px;
        box-shadow: 0 8px 24px var(--nav-shadow);
        flex-direction: column;
        gap: 0;
        padding: 8px;
        min-width: 180px;
        -webkit-backdrop-filter: saturate(140%) blur(8px);
        backdrop-filter: saturate(140%) blur(8px);
    }

    .nav-links.open {
        display: flex;
    }

    .nav-links li a {
        padding: 10px 12px;
    }

    .nav-spacer {
        display: none;
    }

    .hamburger {
        display: inline-flex;
        align-items: center;
        justify-content: center;
    }

    .container {
        padding: 20px;
        margin: 0 10px;
    }

    h1 {
        font-size: 2rem;
    }

    h2 {
        font-size: 1.5rem;
    }
}