:root {
    --font-base: 16px;
    font-size: var(--font-base);
}

[data-fontsize="small"] {
    --font-base: 14px;
}

[data-fontsize="medium"] {
    --font-base: 16px;
}

[data-fontsize="large"] {
    --font-base: 19px;
}

[data-fontsize="xl"] {
    --font-base: 22px;
}

:root,
[data-theme="light"] {
    --bg-page: #ffffff;
    --bg-nav: rgba(255, 255, 255, 0.85);
    --bg-panel2: #FAFAFA;
    --bg-panel: #ffffff;
    --bg-posture: #0a0a0a;

    --text-primary: #0a0a0a;
    --text-muted: rgba(10, 10, 10, 0.55);
    --text-ghost: rgba(10, 10, 10, 0.35);
    --text-on-dark: #ffffff;
    --text-on-dark-muted: rgba(255, 255, 255, 0.65);

    --border-nav: rgba(229, 229, 229, 0.6);
    --border-subtle: #e5e5e5;
    --shadow-panel: 0 8px 32px rgba(0, 0, 0, 0.12);
}

[data-theme="dark"] {
    --bg-page: #171717;
    --bg-nav: rgba(23, 23, 23, 0.9);
    --bg-panel2: #000000;
    --bg-panel: #262626;
    --bg-posture: #0a0a0a;

    --text-primary: #f0f0f0;
    --text-muted: rgba(240, 240, 240, 0.55);
    --text-ghost: rgba(240, 240, 240, 0.3);
    --text-on-dark: #ffffff;
    --text-on-dark-muted: rgba(255, 255, 255, 0.65);

    --border-nav: rgba(255, 255, 255, 0.08);
    --border-subtle: #333333;
    --shadow-panel: 0 8px 32px rgba(0, 0, 0, 0.5);
}

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

body {
    font-family: Inter, sans-serif;
    font-size: var(--font-base);
    background: var(--bg-page);
    color: var(--text-primary);
    transition: background 0.25s, color 0.25s;
}


nav {
    position: sticky;
    top: 0;
    z-index: 100;
    height: 60px;
    background: var(--bg-nav);
    border-bottom: 1px solid var(--border-nav);
    backdrop-filter: blur(12px);
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0 40px;
}

.nav-left {
    display: flex;
    align-items: center;
    gap: 16px;
}

.nav-logo {
    font-size: calc(var(--font-base) * 1.1);
    font-weight: 600;
    color: var(--text-primary);
    letter-spacing: -0.02em;
    min-width: 120px;
    user-select: none;
}

.nav-links {
    display: flex;
    gap: 2px;
}

.nav-links a {
    text-decoration: none;
    font-size: calc(var(--font-base) * 0.875);
    font-weight: 300;
    color: var(--text-muted);
    padding: 7px 14px;
    border-radius: 8px;
    transition: color 0.15s, background 0.15s;
}

.nav-links a:hover {
    color: var(--text-primary);
    background: var(--border-nav);
}

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

.modes {
    display: flex;
    align-items: center;
    gap: 8px;
    min-width: 120px;
    justify-content: flex-end;
    position: relative;
}

.icon-btn {
    background: none;
    border: 1px solid var(--border-subtle);
    border-radius: 8px;
    width: 36px;
    height: 36px;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: background 0.15s;
    flex-shrink: 0;
    color: var(--text-primary);
}

.icon-btn:hover {
    background: var(--border-nav);
}

.icon-btn svg {
    width: 18px;
    height: 18px;
    display: block;
}

.font-panel-wrapper {
    position: relative;
}

.font-panel {
    display: none;
    position: absolute;
    top: calc(100% + 10px);
    right: 0;
    background: var(--bg-panel);
    border: 1px solid var(--border-subtle);
    border-radius: 12px;
    box-shadow: var(--shadow-panel);
    padding: 14px;
    min-width: 170px;
    z-index: 200;
}

.font-panel.open {
    display: block;
    animation: fadeIn 0.15s ease;
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(-4px);
    }

    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.font-panel-title {
    font-size: 11px;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.07em;
    color: var(--text-ghost);
    margin-bottom: 8px;
    padding: 0 4px;
}

.font-options {
    display: flex;
    flex-direction: column;
    gap: 2px;
}

.font-options button {
    background: none;
    border: none;
    border-radius: 8px;
    padding: 8px 12px;
    text-align: left;
    cursor: pointer;
    color: var(--text-primary);
    font-family: inherit;
    font-size: 14px;
    font-weight: 400;
    transition: background 0.12s;
    width: 100%;
}

.font-options button:hover,
.font-options button.active {
    background: var(--border-nav);
    font-weight: 500;
}

.hamburger {
    display: none;
    background: none;
    border: none;
    cursor: pointer;
    width: 30px;
    height: 22px;
    padding: 0;
    flex-direction: column;
    justify-content: space-between;
}

.hamburger span {
    display: block;
    height: 3px;
    background: var(--text-primary);
    border-radius: 2px;
    transition: all 0.3s ease-in-out;
}

.hamburger.active span:nth-child(1) {
    transform: translateY(9px) rotate(45deg);
}

.hamburger.active span:nth-child(2) {
    opacity: 0;
}

.hamburger.active span:nth-child(3) {
    transform: translateY(-9px) rotate(-45deg);
}


.hero {
    min-height: 45vh;
    background: var(--bg-page);
    display: flex;
    align-items: center;
    justify-content: center;
    text-align: center;
}

.hero-content {
    max-width: 700px;
    padding: 80px 24px 60px;
}

.hero h1 {
    font-size: clamp(2.8rem, 6vw, 5rem);
    font-weight: 700;
    letter-spacing: -0.03em;
    line-height: 1.05;
    margin-bottom: 16px;
    color: var(--text-primary);
}

.hero p {
    font-size: clamp(0.95rem, 1.8vw, 1.15rem);
    color: var(--text-muted);
    line-height: 1.6;
}


.panel-light {
    background: var(--bg-panel2);
    padding: 64px 40px;
}

.intro {
    max-width: 960px;
    margin: 0 auto;
}

.intro h2 {
    font-size: clamp(1.4rem, 2.8vw, 2rem);
    font-weight: 600;
    margin-bottom: 16px;
    letter-spacing: -0.02em;
}

.intro p {
    font-size: clamp(0.9rem, 1.5vw, 1rem);
    color: var(--text-muted);
    line-height: 1.7;
    max-width: 680px;
}

.cards-section {
    background: var(--bg-page);
    padding: 60px 40px;
}

.cards-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 40px 60px;
    max-width: 1000px;
    margin: 0 auto;
}

.card-item {
    display: flex;
    flex-direction: column;
}

.card-icon {
    width: 28px;
    height: 28px;
    margin-bottom: 12px;
    color: var(--text-primary);
    opacity: 0.85;
    flex-shrink: 0;
}

.card-item h3 {
    font-size: 1rem;
    font-weight: 600;
    margin-bottom: 10px;
    color: var(--text-primary);
}

.card-item ul {
    list-style: disc;
    padding-left: 18px;
}

.card-item ul li {
    font-size: 0.875rem;
    color: var(--text-muted);
    line-height: 1.6;
    margin-bottom: 4px;
}


.videos {
    background: var(--bg-panel2);
    padding: 60px 40px;
    text-align: center;
}

.videos h2 {
    font-size: clamp(1.8rem, 4vw, 2.8rem);
    font-weight: 700;
    letter-spacing: -0.03em;
    margin-bottom: 40px;
    color: var(--text-primary);
}

.vids {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 30px;
    max-width: 1000px;
    margin: 0 auto;
}

.vid {
    background: var(--bg-panel);
    border-radius: 12px;
    overflow: hidden;
    box-shadow: var(--shadow-panel);
    border: 1px solid var(--border-subtle);
}

.vidbox {
    position: relative;
    width: 100%;
    height: 200px;
}

.vidbox video {
    width: 100%;
    height: 100%;
    object-fit: cover;
}

.vidinfo {
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    background-color: #02020259;
    padding: 20px 16px 16px;
    text-align: left;
}

.vidtext {
    color: white;
    font-size: 0.9rem;
    font-weight: 500;
    display: block;
}


.posture {
    background: var(--bg-posture);
    color: var(--text-on-dark);
    padding: 80px 40px;
}

.posture h2 {
    text-align: center;
    font-size: clamp(1.8rem, 4vw, 2.8rem);
    font-weight: 700;
    letter-spacing: -0.03em;
    margin-bottom: 56px;
}

.posture-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 40px;
    max-width: 860px;
    margin: 0 auto;
}

.posture-col h4 {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-on-dark);
    margin-bottom: 24px;
    letter-spacing: -0.01em;
}

.posture-item {
    display: flex;
    align-items: flex-start;
    gap: 14px;
    margin-bottom: 20px;
}

.posture-icon {
    font-size: 1.3rem;
    line-height: 1;
    flex-shrink: 0;
    width: 28px;
    text-align: center;
}

.posture-text strong {
    display: block;
    font-size: 0.9rem;
    font-weight: 600;
    color: var(--text-on-dark);
    margin-bottom: 2px;
}

.posture-text span {
    font-size: 0.82rem;
    color: var(--text-on-dark-muted);
    line-height: 1.4;
}


.cta {
    background: var(--bg-page);
    padding: 80px 20px;
    text-align: center;
}

.cta h2 {
    font-size: clamp(1.5rem, 3.5vw, 2.4rem);
    font-weight: 700;
    letter-spacing: -0.03em;
    margin-bottom: 12px;
    color: var(--text-primary);
}

.cta p {
    font-size: 0.95rem;
    color: var(--text-muted);
    margin-bottom: 28px;
}

.btn {
    display: inline-block;
    padding: 13px 30px;
    border-radius: 999px;
    background: var(--text-primary);
    color: var(--bg-page);
    font-weight: 600;
    font-size: 0.9rem;
    text-decoration: none;
    transition: transform 0.2s ease, opacity 0.2s ease;
    border: none;
    cursor: pointer;
}

.btn:hover {
    transform: translateY(-2px);
    opacity: 0.85;
}


footer {
    background: var(--bg-panel2);
    border-top: 1px solid var(--border-subtle);
    padding: 48px 40px 32px;
}

.footer-inner {
    max-width: 1000px;
    margin: 0 auto;
    display: grid;
    grid-template-columns: 1.4fr 1fr 1fr;
    gap: 40px;
}

.footer-brand strong {
    display: block;
    font-size: 0.95rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 10px;
}

.footer-brand p {
    font-size: 0.82rem;
    color: var(--text-muted);
    line-height: 1.6;
    max-width: 220px;
}

.footer-col h5 {
    font-size: 0.82rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 12px;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.footer-col a {
    display: block;
    font-size: 0.82rem;
    color: var(--text-muted);
    text-decoration: none;
    margin-bottom: 8px;
    transition: color 0.15s;
}

.footer-col a:hover {
    color: var(--text-primary);
}

.footer-info-text {
    font-size: 0.82rem;
    color: var(--text-muted);
    line-height: 1.6;
}

.footer-bottom {
    max-width: 1000px;
    margin: 32px auto 0;
    padding-top: 20px;
    border-top: 1px solid var(--border-subtle);
    text-align: center;
    font-size: 0.78rem;
    color: var(--text-ghost);
}

@media (max-width: 1024px) {
    .cards-grid {
        grid-template-columns: repeat(2, 1fr);
        gap: 32px 48px;
    }

    .vids {
        grid-template-columns: repeat(2, 1fr);
        gap: 25px;
    }

    .posture-grid {
        grid-template-columns: 1fr;
    }
}

@media (max-width: 768px) {
    nav {
        padding: 12px 14px;
        flex-wrap: wrap;
        gap: 10px;
        height: auto;
        align-items: center;
        justify-content: space-between;
    }

    .nav-left {
        flex: 1 1 auto;
        min-width: 0;
        justify-content: flex-start;
    }

    .hamburger {
        display: flex;
        position: static;
        transform: none;
        margin-left: 0;
    }

    .nav-links {
        order: 2;
        width: 100%;
        display: none;
        flex-direction: column;
        gap: 8px;
        background: var(--bg-panel);
        border: 1px solid var(--border-subtle);
        border-radius: 10px;
        padding: 10px;
        margin-top: 8px;
    }

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

    .nav-links a {
        padding: 8px 10px;
        font-size: calc(var(--font-base) * 0.9);
    }

    .modes {
        order: 1;
        flex: 0 1 auto;
        justify-content: flex-end;
    }

    .cards-section {
        padding: 40px 20px;
    }

    .cards-grid {
        grid-template-columns: 1fr;
        gap: 28px;
    }

    .posture {
        padding: 60px 20px;
    }

    .videos {
        padding: 40px 20px;
    }

    .vids {
        grid-template-columns: 1fr;
        gap: 20px;
    }

    .footer-inner {
        grid-template-columns: 1fr;
        gap: 28px;
    }
}

@media (max-width: 480px) {
    .hero-content {
        padding: 45px 16px;
    }

    .nav-links a {
        font-size: calc(var(--font-base) * 0.75);
        padding: 7px 8px;
    }

    .btn {
        width: 100%;
        max-width: 280px;
    }
}