/* ═══════════════════════════════════════════════
   btn-up-to-top — volver al inicio de la página
   Posición: centro col 12 @ 1280 · última col en resto
   ═══════════════════════════════════════════════ */

.btn-up-to-top {
    --uptotop-col: 4;
    --uptotop-frame-max: 100vw;
    --uptotop-col-width: calc(
        (min(100vw, var(--uptotop-frame-max)) - 2 * var(--grid-margin) - (var(--grid-columns) - 1) * var(--grid-gutter))
        / var(--grid-columns)
    );
    --uptotop-frame-offset: max(0px, (100vw - var(--uptotop-frame-max)) / 2);

    box-sizing: border-box;
    position: fixed;
    bottom: 38px;
    left: calc(
        var(--uptotop-frame-offset)
        + var(--grid-margin)
        + (var(--uptotop-col) - 1) * (var(--uptotop-col-width) + var(--grid-gutter))
        + var(--uptotop-col-width) / 2
    );
    z-index: 10000;
    transform: translateX(-50%);

    display: flex;
    flex-direction: row;
    justify-content: center;
    align-items: center;
    width: 54px;
    height: 54px;
    padding: 15px;
    border: 1px solid transparent;
    border-radius: 27px;
    background: var(--grey-70);
    box-shadow: 0 4px 4px rgba(0, 0, 0, 0.2);
    cursor: pointer;
    font-family: var(--serif);

    opacity: 0;
    visibility: hidden;
    pointer-events: none;
    transition:
        opacity 0.25s ease,
        visibility 0.25s ease,
        background-color 0.2s ease,
        border-color 0.2s ease,
        color 0.2s ease;
}

.btn-up-to-top.is-visible {
    opacity: 1;
    visibility: visible;
    pointer-events: auto;
}

.btn-up-to-top__icon {
    font-family: var(--serif);
    font-size: 24px;
    line-height: 1;
    font-weight: 300;
    color: var(--grey-10);
}

.btn-up-to-top:hover {
    background: var(--grey-0);
    border-color: var(--grey-40);
}

.btn-up-to-top:hover .btn-up-to-top__icon {
    color: var(--grey-40);
}

.btn-up-to-top:active {
    background: var(--grey-10);
    border-color: var(--grey-40);
}

.btn-up-to-top:active .btn-up-to-top__icon {
    color: var(--grey-40);
}

.btn-up-to-top:focus {
    outline: none;
}

.btn-up-to-top:focus-visible {
    outline: 2px solid var(--grey-70);
    outline-offset: 3px;
}

@media (min-width: 768px) {
    .btn-up-to-top {
        --uptotop-col: 8;
    }
}

@media (min-width: 1024px) {
    .btn-up-to-top {
        --uptotop-col: 12;
    }
}

@media (min-width: 1280px) {
    .btn-up-to-top {
        --uptotop-col: 12;
        --uptotop-frame-max: var(--grid-frame-max);
    }
}