/* Gauss AI - Layout v2.0
   Header (w/ mobile nav), footer 4-column grid */

/* === Header === */
.header {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    z-index: 200;
    padding: 0 var(--space-4);
    height: var(--header-height);
    background: rgba(255,255,255,0.92);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    border-bottom: 1px solid var(--color-border);
    transition: height var(--duration-base) var(--ease-out),
                box-shadow var(--duration-base);
}

.header--scrolled {
    height: var(--header-height-shrink);
    box-shadow: var(--shadow-sm);
}

.header__inner {
    max-width: var(--container-max);
    margin: 0 auto;
    height: 100%;
    display: flex;
    align-items: center;
    justify-content: space-between;
}

/* Logo */
.header__logo img {
    height: 36px;
    width: auto;
    display: block;
}

/* Desktop nav */
.header__nav {
    display: flex;
    gap: var(--space-5);
}

.header__nav a {
    font-size: var(--text-sm);
    font-weight: 500;
    color: var(--color-text-secondary);
    transition: color var(--duration-fast);
}

.header__nav a:hover {
    color: var(--color-text);
}

/* Right side */
.header__actions {
    display: flex;
    align-items: center;
    gap: var(--space-2);
}

.lang-toggle {
    font-size: var(--text-sm);
    font-weight: 600;
    color: var(--color-text-secondary);
    padding: 0.35rem 0.7rem;
    border-radius: var(--radius-sm);
    transition: all var(--duration-fast);
}

.lang-toggle:hover {
    color: var(--color-text);
    background: var(--color-bg-subtle);
}

/* Hamburger button */
.hamburger {
    display: none;
    background: none;
    border: none;
    cursor: pointer;
    padding: 0.5rem;
    z-index: 300;
}

.hamburger__line {
    display: block;
    width: 22px;
    height: 2px;
    background: var(--color-text);
    border-radius: 1px;
    transition: all var(--duration-base) var(--ease-out);
}

.hamburger__line + .hamburger__line {
    margin-top: 6px;
}

.hamburger[aria-expanded="true"] .hamburger__line:nth-child(1) {
    transform: rotate(45deg) translate(3px, 3px);
}

.hamburger[aria-expanded="true"] .hamburger__line:nth-child(2) {
    opacity: 0;
}

.hamburger[aria-expanded="true"] .hamburger__line:nth-child(3) {
    transform: rotate(-45deg) translate(4px, -4px);
}

/* Mobile nav overlay */
.mobile-nav {
    display: none;
    position: fixed;
    inset: 0;
    z-index: 250;
    background: var(--gauss-white);
    padding: calc(var(--header-height) + var(--space-4)) var(--space-4) var(--space-4);
    flex-direction: column;
    gap: var(--space-1);
    opacity: 0;
    transform: translateY(-10px);
    transition: opacity var(--duration-base) var(--ease-out),
                transform var(--duration-base) var(--ease-out);
}

.mobile-nav.is-open {
    display: flex;
    opacity: 1;
    transform: translateY(0);
}

.mobile-nav a {
    display: block;
    padding: var(--space-2) 0;
    font-size: 1.25rem;
    font-weight: 600;
    font-family: var(--font-brand);
    color: var(--color-text);
    border-bottom: 1px solid var(--color-border);
    transition: color var(--duration-fast);
}

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

.mobile-nav .btn {
    margin-top: var(--space-4);
    justify-content: center;
}

/* Body scroll lock */
body.nav-open {
    overflow: hidden;
}

/* === Footer === */
.footer {
    background: var(--gauss-ink-900);
    color: var(--gauss-white);
    padding: var(--space-8) 0 var(--space-4);
}

.footer__grid {
    max-width: var(--container-max);
    margin: 0 auto;
    padding: 0 var(--space-4);
    display: grid;
    grid-template-columns: 2fr 1fr 1fr 1fr;
    gap: var(--space-6);
}

.footer__brand p {
    margin-top: var(--space-2);
    color: rgba(255,255,255,0.5);
    font-size: var(--text-sm);
    max-width: 280px;
    line-height: 1.6;
}

.footer__brand img {
    height: 32px;
    width: auto;
}

.footer__col h4 {
    font-size: var(--text-sm);
    font-weight: 600;
    margin-bottom: var(--space-3);
    color: rgba(255,255,255,0.9);
    letter-spacing: 0;
}

.footer__col a {
    display: block;
    padding: 0.3rem 0;
    font-size: var(--text-sm);
    color: rgba(255,255,255,0.5);
    transition: color var(--duration-fast);
}

.footer__col a:hover {
    color: var(--gauss-white);
}

.footer__bottom {
    max-width: var(--container-max);
    margin: var(--space-6) auto 0;
    padding: var(--space-3) var(--space-4) 0;
    border-top: 1px solid rgba(255,255,255,0.08);
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.footer__copy {
    font-size: var(--text-xs);
    color: rgba(255,255,255,0.35);
}

.footer__legal {
    max-width: var(--container-max);
    margin: var(--space-3) auto 0;
    padding: 0 var(--space-4);
    text-align: center;
}

.footer__legal p {
    font-size: var(--text-xs);
    color: rgba(255,255,255,0.25);
    line-height: 1.6;
}

/* === Footer: Gauss number highlight === */
.footer__gauss-number {
    display: inline-flex;
    align-items: center;
    gap: 0.4rem;
    padding: 0.4rem 0.8rem;
    background: rgba(37,211,102,0.15);
    border-radius: var(--radius-pill);
    color: #25D366 !important;
    font-weight: 600;
    font-size: var(--text-sm);
    margin-bottom: 0.5rem;
    transition: background var(--duration-fast);
}

.footer__gauss-number:hover {
    background: rgba(37,211,102,0.25);
    color: #25D366 !important;
}

.footer__gauss-number svg {
    flex-shrink: 0;
}

.footer__support-label {
    display: block;
    font-size: var(--text-xs);
    color: rgba(255,255,255,0.35);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    margin-top: var(--space-2);
    margin-bottom: 0.25rem;
}

/* === Responsive === */
@media (max-width: 968px) {
    .header__nav {
        display: none;
    }

    .hamburger {
        display: block;
    }

    .header__actions .btn {
        display: none;
    }

    .footer__grid {
        grid-template-columns: 1fr 1fr;
        gap: var(--space-4);
    }

    .footer__brand {
        grid-column: 1 / -1;
    }

    .footer__bottom {
        flex-direction: column;
        gap: var(--space-2);
        text-align: center;
    }
}

@media (max-width: 480px) {
    .footer__grid {
        grid-template-columns: 1fr;
    }
}