/* ==========================================================================
   Navigation — Sticky Header + Mobile Overlay
   ========================================================================== */

/* --- Header --- */
.site-header {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 100;
    background: var(--color-nav-bg);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    border-bottom: 1px solid var(--color-border);
    transition: background-color var(--transition-base);
}

.site-nav {
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 72px;
}

/* --- Logo --- */
.nav-logo {
    text-decoration: none;
    color: var(--color-text);
    transition: color var(--transition-fast);
}

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

.nav-logo-text {
    font-family: var(--font-display);
    font-size: var(--text-lg);
    letter-spacing: 0.05em;
}

/* --- Links --- */
.nav-links {
    display: flex;
    list-style: none;
    gap: var(--space-md);
}

.nav-link {
    font-family: var(--font-body);
    font-size: var(--text-sm);
    font-weight: 500;
    color: var(--color-text-secondary);
    text-decoration: none;
    padding: var(--space-xs) 0;
    position: relative;
    transition: color var(--transition-fast);
}

.nav-link::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    width: 0;
    height: 2px;
    background: var(--color-accent);
    transition: width var(--transition-base);
}

.nav-link:hover,
.nav-link.is-active {
    color: var(--color-text);
}

.nav-link.is-active::after,
.nav-link:hover::after {
    width: 100%;
}

/* --- Actions --- */
.nav-actions {
    display: flex;
    align-items: center;
    gap: var(--space-sm);
}

/* --- Theme Toggle --- */
.theme-toggle {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 40px;
    height: 40px;
    border-radius: var(--radius-sm);
    color: var(--color-text-secondary);
    transition: color var(--transition-fast), background-color var(--transition-fast);
}

.theme-toggle:hover {
    color: var(--color-text);
    background: var(--color-surface);
}

/* Initial state — JS sets correct visibility */
.icon-sun { display: none; }
.icon-moon { display: block; }

/* --- CTA Button --- */
.nav-cta {
    font-family: var(--font-body);
    font-size: var(--text-sm);
    font-weight: 700;
    color: #0A0A0A;
    background: var(--color-accent);
    padding: 0.5rem 1.25rem;
    border-radius: var(--radius-sm);
    text-decoration: none;
    transition: background-color var(--transition-fast), transform var(--transition-fast);
}

.nav-cta:hover {
    background: var(--color-accent-hover);
    color: #0A0A0A;
    transform: translateY(-1px);
}

/* --- Hamburger --- */
.menu-toggle {
    display: none;
    flex-direction: column;
    justify-content: center;
    gap: 5px;
    width: 40px;
    height: 40px;
    padding: 8px;
}

.menu-toggle-bar {
    display: block;
    width: 100%;
    height: 2px;
    background: var(--color-text);
    transition: transform var(--transition-base), opacity var(--transition-base);
}

.menu-toggle.is-open .menu-toggle-bar:nth-child(1) {
    transform: rotate(45deg) translate(5px, 5px);
}

.menu-toggle.is-open .menu-toggle-bar:nth-child(2) {
    opacity: 0;
}

.menu-toggle.is-open .menu-toggle-bar:nth-child(3) {
    transform: rotate(-45deg) translate(5px, -5px);
}

/* --- Mobile Overlay --- */
.mobile-overlay {
    position: fixed;
    inset: 0;
    z-index: 99;
    background: var(--color-bg);
    display: flex;
    align-items: center;
    justify-content: center;
    opacity: 0;
    visibility: hidden;
    transition: opacity var(--transition-base), visibility var(--transition-base);
}

.mobile-overlay.is-open {
    opacity: 1;
    visibility: visible;
}

.mobile-nav-links {
    list-style: none;
    text-align: center;
}

.mobile-nav-links li {
    margin-bottom: var(--space-md);
}

.mobile-nav-links a {
    font-family: var(--font-display);
    font-size: var(--text-2xl);
    color: var(--color-text);
    text-decoration: none;
    text-transform: uppercase;
    transition: color var(--transition-fast);
}

.mobile-nav-links a:hover {
    color: var(--color-accent);
}

/* --- Responsive --- */
@media (max-width: 900px) {
    .nav-links {
        display: none;
    }

    .nav-cta {
        display: none;
    }

    .menu-toggle {
        display: flex;
    }
}