/* Header */
header {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    z-index: var(--z-sticky);
    background: rgba(var(--bg-primary), 0.8);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--border-color);
    transition: all var(--transition-base);
}

/* Main Navigation */
.main-nav {
    display: flex;
    justify-content: space-between;
    align-items: center;
    height: 70px;
    padding: 0 var(--space-xl);
    max-width: 1400px;
    margin: 0 auto;
}

/* Logo */
.logo {
    font-size: var(--font-size-2xl);
    font-weight: 700;
    color: var(--text-color);
    text-decoration: none;
    display: flex;
    align-items: center;
    gap: var(--space-xs);
}

.logo-text {
    color: var(--accent-color);
}

.logo-sys {
    background: linear-gradient(
        135deg,
        var(--accent-color) 0%,
        var(--accent-purple) 100%
    );
    -webkit-background-clip: text;
    background-clip: text;
    color: transparent;
}

/* Navigation Controls */
.nav-controls {
    display: flex;
    align-items: center;
    gap: var(--space-md);
}

/* Theme Toggle */
#theme-toggle {
    background: transparent;
    border: none;
    color: var(--text-color);
    width: 40px;
    height: 40px;
    border-radius: var(--border-radius-full);
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    transition: all var(--transition-base);
}

#theme-toggle:hover {
    background: var(--card-bg);
}

#theme-toggle i {
    font-size: var(--font-size-lg);
    transition: transform var(--transition-base);
}

#theme-toggle:hover i {
    transform: rotate(15deg);
}

/* Scroll Progress */
.scroll-progress {
    position: absolute;
    bottom: -2px;
    left: 0;
    width: 100%;
    height: 2px;
    background: var(--accent-color);
    transform-origin: left;
    transform: scaleX(0);
    transition: transform var(--transition-base);
}

/* Header Scroll State */
header.scrolled {
    box-shadow: var(--shadow-md);
    background: var(--bg-primary);
}

/* Skip Link */
.skip-link {
    position: fixed;
    top: -100%;
    left: 50%;
    transform: translateX(-50%);
    background: var(--accent-color);
    color: white;
    padding: var(--space-sm) var(--space-md);
    border-radius: 0 0 var(--border-radius-md) var(--border-radius-md);
    text-decoration: none;
    z-index: var(--z-maximum);
    transition: top var(--transition-base);
}

.skip-link:focus {
    top: 0;
}

/* Responsive Design */
@media (max-width: 768px) {
    .main-nav {
        padding: 0 var(--space-md);
    }

    .logo {
        font-size: var(--font-size-xl);
    }
}

/* High Contrast Mode */
@media (forced-colors: active) {
    header {
        border-bottom: 1px solid CanvasText;
    }

    .logo-text,
    .logo-sys {
        background: none;
        color: CanvasText;
    }
}

/* Reduced Motion */
@media (prefers-reduced-motion: reduce) {
    header,
    .scroll-progress,
    #theme-toggle,
    .skip-link {
        transition: none;
    }

    #theme-toggle:hover i {
        transform: none;
    }
}

/* Dark Theme Specific */
.dark-theme header {
    background: rgba(10, 10, 10, 0.8);
}

/* Light Theme Specific */
.light-theme header {
    background: rgba(242, 242, 242, 0.8);
}