/* ================================
   Design Tokens
================================ */
:root {
    --color-bg: #ffffff;
    --color-bg-sub: #f7f7f7;
    --color-text: #1a1a1a;
    --color-text-sub: #6b6b6b;
    --color-border: #e5e5e5;
    --color-accent: #0a4d8c;

    --font-ja: "Yu Gothic", "YuGothic", "Hiragino Kaku Gothic ProN", "ヒラギノ角ゴ ProN W3", "メイリオ", "Meiryo", sans-serif;
    --font-en: "Inter", system-ui, -apple-system, "Segoe UI", "Helvetica Neue", sans-serif;
    --font-base: "Inter", "Yu Gothic", "YuGothic", "Hiragino Kaku Gothic ProN", "ヒラギノ角ゴ ProN W3", "メイリオ", "Meiryo", system-ui, -apple-system, sans-serif;

    --header-height: 72px;
    --header-height-sm: 60px;
    --content-max: 1040px;
    --content-pad: clamp(24px, 5vw, 80px);
    --section-pad: clamp(72px, 12vh, 140px);

    --ease: cubic-bezier(0.2, 0.7, 0.2, 1);
}

/* ================================
   Base
================================ */
body {
    font-family: var(--font-base);
    font-weight: 400;
    font-size: 15px;
    line-height: 1.8;
    color: var(--color-text);
    background-color: var(--color-bg);
    letter-spacing: 0.02em;
}

/* ================================
   Layout helpers
================================ */
.container {
    width: 100%;
    max-width: var(--content-max);
    margin-inline: auto;
    padding-inline: var(--content-pad);
}

.section {
    padding-block: var(--section-pad);
}

.section--sub {
    background-color: var(--color-bg-sub);
}

.section__label {
    font-family: var(--font-en);
    font-size: 12px;
    font-weight: 500;
    letter-spacing: 0.2em;
    color: var(--color-text-sub);
    text-transform: uppercase;
    margin-bottom: 16px;
    display: block;
}

.section__title {
    font-family: var(--font-ja);
    font-size: clamp(1.4rem, 2.8vw, 1.875rem);
    font-weight: 500;
    line-height: 1.5;
    letter-spacing: 0.05em;
    margin-bottom: clamp(32px, 5vw, 56px);
}

/* ================================
   Header
================================ */
.site-header {
    position: fixed;
    inset: 0 0 auto 0;
    height: var(--header-height);
    z-index: 50;
    background-color: rgba(255, 255, 255, 0.8);
    backdrop-filter: saturate(1.2) blur(12px);
    -webkit-backdrop-filter: saturate(1.2) blur(12px);
    border-bottom: 1px solid transparent;
    transition: height 0.3s var(--ease), border-color 0.3s var(--ease), background-color 0.3s var(--ease);
}

.site-header.is-scrolled {
    border-bottom-color: var(--color-border);
}

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

.site-header__title {
    font-family: var(--font-ja);
    font-size: 15px;
    font-weight: 500;
    letter-spacing: 0.08em;
    line-height: 1;
}

.site-header__title a {
    display: inline-flex;
    align-items: center;
    color: var(--color-text);
}

.site-header__logo {
    display: block;
    width: auto;
    height: 44px;
    color: var(--color-text);
}

.site-nav__list {
    display: flex;
    gap: clamp(20px, 3vw, 40px);
    align-items: center;
}

.site-nav__list a {
    font-family: var(--font-en);
    font-size: 12px;
    font-weight: 500;
    letter-spacing: 0.15em;
    color: var(--color-text-sub);
    transition: color 0.2s var(--ease);
    position: relative;
}

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

.site-nav__list a::after {
    content: "";
    position: absolute;
    left: 0;
    right: 0;
    bottom: -6px;
    height: 1px;
    background-color: currentColor;
    transform: scaleX(0);
    transform-origin: left;
    transition: transform 0.3s var(--ease);
}

.site-nav__list a:hover::after {
    transform: scaleX(1);
}

/* Hamburger */
.site-nav__toggle {
    display: none;
    width: 32px;
    height: 32px;
    position: relative;
    z-index: 60;
}

.site-nav__toggle span {
    position: absolute;
    left: 4px;
    right: 4px;
    height: 1px;
    background-color: var(--color-text);
    transition: transform 0.3s var(--ease), opacity 0.3s var(--ease), top 0.3s var(--ease);
}

.site-nav__toggle span:nth-child(1) { top: 11px; }
.site-nav__toggle span:nth-child(2) { top: 16px; }
.site-nav__toggle span:nth-child(3) { top: 21px; }

.site-nav__toggle[aria-expanded="true"] span:nth-child(1) {
    top: 16px;
    transform: rotate(45deg);
}
.site-nav__toggle[aria-expanded="true"] span:nth-child(2) { opacity: 0; }
.site-nav__toggle[aria-expanded="true"] span:nth-child(3) {
    top: 16px;
    transform: rotate(-45deg);
}

/* ================================
   Certification
================================ */
.certification {
    background-color: var(--color-bg-sub);
    border-top: 1px solid var(--color-border);
    padding-block: clamp(40px, 6vw, 64px);
}

.certification__inner {
    width: 100%;
    max-width: var(--content-max);
    margin-inline: auto;
    padding-inline: var(--content-pad);
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: clamp(24px, 4vw, 56px);
    flex-wrap: wrap;
}

.certification__text {
    flex: 1 1 420px;
    min-width: 0;
}

.certification__eyebrow {
    font-family: var(--font-en);
    font-size: 11px;
    font-weight: 500;
    letter-spacing: 0.25em;
    text-transform: uppercase;
    color: var(--color-text-sub);
    margin-bottom: 10px;
}

.certification__lead {
    font-family: var(--font-ja);
    font-size: 13px;
    line-height: 1.95;
    color: var(--color-text-sub);
    max-width: 620px;
}

.certification__mark {
    flex: 0 0 auto;
}

.certification__mark img {
    display: block;
    width: clamp(220px, 20vw, 260px);
    height: auto;
}

@media (max-width: 767px) {
    .certification__inner {
        flex-direction: column;
        align-items: flex-start;
        justify-content: flex-start;
        gap: 24px;
    }
    .certification__text {
        flex: 0 1 auto;
    }
    .certification__mark img {
        width: min(240px, 72vw);
    }
}

/* ================================
   Footer
================================ */
.site-footer {
    border-top: 1px solid var(--color-border);
    padding-block: 40px;
    background-color: var(--color-bg);
}

.site-footer__inner {
    width: 100%;
    max-width: var(--content-max);
    margin-inline: auto;
    padding-inline: var(--content-pad);
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 16px;
    flex-wrap: wrap;
}

.site-footer__copy {
    font-family: var(--font-en);
    font-size: 11px;
    letter-spacing: 0.1em;
    color: var(--color-text-sub);
}

.site-footer__policy {
    font-size: 12px;
    color: var(--color-text-sub);
    transition: color 0.2s var(--ease);
}

.site-footer__policy:hover {
    color: var(--color-text);
}

/* ================================
   Return top button
================================ */
.return-top {
    position: fixed;
    right: clamp(16px, 3vw, 32px);
    bottom: clamp(16px, 3vw, 32px);
    width: 44px;
    height: 44px;
    border: 1px solid var(--color-border);
    background-color: rgba(255, 255, 255, 0.9);
    backdrop-filter: blur(8px);
    -webkit-backdrop-filter: blur(8px);
    border-radius: 50%;
    display: grid;
    place-items: center;
    opacity: 0;
    pointer-events: none;
    transition: opacity 0.3s var(--ease), transform 0.3s var(--ease);
    z-index: 40;
}

.return-top.is-visible {
    opacity: 1;
    pointer-events: auto;
}

.return-top:hover {
    transform: translateY(-2px);
}

.return-top::before {
    content: "";
    width: 8px;
    height: 8px;
    border-top: 1px solid var(--color-text);
    border-right: 1px solid var(--color-text);
    transform: rotate(-45deg);
    margin-top: 4px;
}

/* ================================
   Fade-in animation
================================ */
.fade-in {
    opacity: 0;
    transform: translateY(16px);
    transition: opacity 0.8s var(--ease), transform 0.8s var(--ease);
}

.fade-in.is-visible {
    opacity: 1;
    transform: translateY(0);
}

@media (prefers-reduced-motion: reduce) {
    .fade-in {
        opacity: 1;
        transform: none;
        transition: none;
    }
}

/* ================================
   Responsive (mobile)
================================ */
@media (max-width: 767px) {
    :root {
        --header-height: var(--header-height-sm);
        --section-pad: clamp(56px, 10vh, 100px);
    }

    body {
        font-size: 14px;
        line-height: 1.75;
    }

    .site-header__logo {
        height: 36px;
    }

    .site-nav__toggle {
        display: block;
    }

    .site-nav__list {
        position: fixed;
        top: var(--header-height-sm);
        left: 0;
        right: 0;
        bottom: 0;
        width: 100vw;
        height: calc(100dvh - var(--header-height-sm));
        background-color: var(--color-bg);
        flex-direction: column;
        justify-content: center;
        align-items: center;
        gap: 32px;
        z-index: 55;
        opacity: 0;
        pointer-events: none;
        overflow-y: auto;
        transition: opacity 0.3s var(--ease);
    }

    .site-nav__list.is-open {
        opacity: 1;
        pointer-events: auto;
    }

    .site-nav__list a {
        font-size: 14px;
        letter-spacing: 0.2em;
    }

    .site-footer__inner {
        flex-direction: column;
        text-align: center;
    }
}