/* Back to top — pure CSS */

.back-to-top {
    position: fixed;
    inset-block-end: 0; /* bottom */
    inset-inline-end: 40px; /* right */

    display: grid;
    place-items: center;

    inline-size: 50px;
    block-size: 50px;

    background: #2563eb; /* primary */
    color: #ffffff; /* textWhite */
    text-decoration: none;
    border-radius: 50%;

    opacity: 0;
    transform: scale(0.3);
    box-shadow: 0 4px 10px rgba(0, 0, 0, 0.25);

    z-index: 990; /* overlay-ish */

    transition: opacity 250ms ease,
    transform 250ms ease,
    inset-block-end 250ms ease;
}

.back-to-top:focus-visible {
    outline: 2px solid #2563eb;
    outline-offset: 2px;
}

.back-to-top:focus {
    color: #ffffff;
}

.back-to-top.show {
    inset-block-end: 40px;
    inset-inline-end: 40px;
    opacity: 1;
    transform: scale(1);
}

.back-to-top.show:hover {
    color: #ffffff;
    inset-block-end: 50px;
}

.arrow {
    position: absolute;
    inline-size: 12px;
    block-size: 12px;
    background-image: url(data:image/svg+xml;base64,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);
    background-size: contain;
    background-repeat: no-repeat;

    transform: rotate(-90deg);
    inset-block-start: 30%;
    inset-inline-start: 40%;
}

.arrow:nth-child(2) {
    inset-block-start: 42%;
}

@keyframes bounceAlpha {
    0% {
        opacity: 1;
        transform: rotate(-90deg) translateX(0) scale(1);
    }
    25% {
        opacity: 0;
        transform: rotate(-90deg) translateX(10px) scale(0.9);
    }
    26% {
        opacity: 0;
        transform: rotate(-90deg) translateX(-10px) scale(0.9);
    }
    55% {
        opacity: 1;
        transform: rotate(-90deg) translateX(0) scale(1);
    }
}

.back-to-top:hover .arrow {
    animation: bounceAlpha 1.4s linear infinite;
}

.back-to-top:hover .arrow:nth-child(2) {
    animation-delay: 0.2s;
}

/* Mobile tweaks (przyjąłem 480px jako "xs") */
@media (max-width: 480px) {
    .back-to-top {
        inline-size: 40px;
        block-size: 40px;
        line-height: 40px;
    }

    .back-to-top.show {
        inset-block-end: 10px;
        inset-inline-end: 10px;
    }

    .back-to-top.show:hover {
        inset-block-end: 10px;
    }

    .arrow {
        inset-block-start: 27%;
        inset-inline-start: 37%;
    }
}

/* Reduced motion */
@media (prefers-reduced-motion: reduce) {
    .back-to-top,
    .back-to-top.show {
        transition: none !important;
    }

    .back-to-top:hover .arrow {
        animation: none !important;
    }
}

/* Forced colors / High contrast */
@media (forced-colors: active) {
    .back-to-top {
        background: Canvas;
        color: CanvasText;
        border: 1px solid CanvasText;
        box-shadow: none;
    }
}