/*
vars
*/
:root {
    --carousel-transition-duration: 250ms;
    --carousel-transition-ease: ease-out;
    --carousel-bg-color-rgb: 0, 0, 0;
    --carousel-shadow-color-rgb: 128, 128, 128;
    --carousel-item-width: 11.5rem;
    --carousel-item-height: 17.5rem;
    --carousel-item-hover-effect: 1.075;
    --carousel-item-reflection-blur: 0.25rem;
    --carousel-item-empty-color-rgb: 255, 255, 255;
    --carousel-item-glow-color-rgb: 255, 255, 255;
    --carousel-item-glow-size: 5rem;
    --carousel-diameter: 50rem;
    --carousel-3d-perspective: 1000px;
    --carousel-3d-perspective-origin: 50% 20%;
    --carousel-control-button-width: 1.25rem;
    --carousel-control-button-height: 4rem;
    --carousel-control-color-rgb: 255, 255, 255;
    --carousel-animation-duration: 25s;
    --carousel-animation-play-state: running;
    --carousel-direction-animation-play-state: paused;
}

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

*:focus {
    outline: none;
}

a {
    -webkit-tap-highlight-color: rgba(0, 0, 0, 0);
    -webkit-tap-highlight-color: transparent;
    -webkit-user-select: none;
    -khtml-user-select: none;
    -moz-user-select: none;
    -ms-user-select: none;
    user-select: none;
}

body {
    display: flex;
    align-items: center;
    justify-content: center;
    height: 100vh;
    background-color: rgb(var(--carousel-bg-color-rgb));
    overflow: hidden;
}

/*
carousel
*/
.carousel {
    --_diameter: var(--carousel-diameter);
    --_radius: calc(var(--_diameter) / 2);
    --_item-width: var(--carousel-item-width);
    --_item-height: var(--carousel-item-height);
    perspective: var(--carousel-3d-perspective);
    perspective-origin: var(--carousel-3d-perspective-origin);
    width: var(--_diameter);
    height: var(--_diameter);
}

@media only screen and (max-width: 48rem) {
    .carousel {
        --_diameter: calc(var(--carousel-diameter) * 0.75);
        --_item-width: calc(var(--carousel-item-width) * 0.75);
        --_item-height: calc(var(--carousel-item-height) * 0.75);
    }
}

@media only screen and (max-width: 32rem) {
    .carousel {
        --_diameter: calc(var(--carousel-diameter) * 0.6);
        --_item-width: calc(var(--carousel-item-width) * 0.6);
        --_item-height: calc(var(--carousel-item-height) * 0.6);
    }
}

@media only screen and (max-width: 16rem) {
    .carousel {
        --_diameter: calc(var(--carousel-diameter) * 0.25);
        --_item-width: calc(var(--carousel-item-width) * 0.25);
        --_item-height: calc(var(--carousel-item-height) * 0.25);
    }
}

.carousel .carousel-control-button {
    --_width: var(--carousel-control-button-width);
    --_height: var(--carousel-control-button-height);
    z-index: 1;
    width: var(--_width);
    height: var(--_height);
    background-color: rgb(var(--carousel-control-color-rgb));
    opacity: 0.2;
    transition: opacity var(--carousel-transition-duration) var(--carousel-transition-ease);
    position: absolute;
}
.carousel .carousel-control-button:hover {
    opacity: 0.4;
}
.carousel .carousel-control-button:has(input:checked) {
    opacity: 0.8;
}

.carousel .carousel-control-button input {
    -webkit-appearance: none;
    appearance: none;
    opacity: 0;
    width: 100%;
    height: 100%;
    cursor: pointer;
}

.carousel .carousel-control-button.left {
    clip-path: polygon(0% 50%, 100% 0%, 100% 100%);
    top: calc(var(--_radius) - var(--_height) / 2);
    left: 0;
}
.carousel:has(.carousel-control-button.left input:checked) {
    --carousel-direction-animation-play-state: running;
}

.carousel .carousel-control-button.right {
    clip-path: polygon(0% 0%, 100% 50%, 0% 100%);
    top: calc(var(--_radius) - var(--_height) / 2);
    right: 0;
}
.carousel:has(.carousel-control-button.right input:checked) {
    --carousel-direction-animation-play-state: paused;
}

.carousel .carousel-rotation-direction {
    --_direction-animation-play-state: var(--carousel-direction-animation-play-state);
    --_z: calc(var(--_radius) * -1);
    transform: translateZ(var(--_z));
    transform-style: preserve-3d;
    animation: carousel-rotation-reverse calc(var(--carousel-animation-duration) / 2) reverse linear infinite var(--_direction-animation-play-state);
    transition: all var(--carousel-transition-duration) var(--carousel-transition-ease);
}

@keyframes carousel-rotation-reverse {
    from {transform: translateZ(var(--_z)) rotateY(0deg);}
    to {transform: translateZ(var(--_z)) rotateY(360deg);}
}

@keyframes carousel-rotation-normal {
    from {transform: rotateY(0deg);}
    to {transform: rotateY(360deg);}
}

.carousel .carousel-item-wrapper {
    transform-style: inherit;
    width: inherit;
    height: inherit;
    list-style-type: none;
    position: relative;
    animation: carousel-rotation-normal var(--carousel-animation-duration) normal linear infinite var(--carousel-animation-play-state);
    transition: all var(--carousel-transition-duration) var(--carousel-transition-ease);
}

.carousel .carousel-rotation-direction:has(.carousel-item:hover) {
    --carousel-animation-play-state: paused;
    --_direction-animation-play-state: paused;
}

.carousel .carousel-item {
    --_width: var(--_item-width);
    --_height: var(--_item-height);
    --_rotation: calc(360 / var(--_num-elements) * var(--_index) * 1deg);
    left: calc(var(--_radius) - var(--_item-width) / 2);
    top: calc(var(--_radius) - var(--_item-height) / 2);
    transform: rotateY(var(--_rotation)) translateZ(var(--_radius));
    transform-style: inherit;
    width: var(--_width);
    height: var(--_height);
    transition: all var(--carousel-transition-duration) var(--carousel-transition-ease);
    box-shadow: 0 0 var(--carousel-item-glow-size) transparent;
    position: absolute;
}

.carousel .carousel-item:hover {
    box-shadow: 0 0 var(--carousel-item-glow-size) rgb(var(--carousel-item-glow-color-rgb));
    transform: rotateY(var(--_rotation)) translateZ(calc(var(--_radius) * var(--carousel-item-hover-effect)));
}

.carousel .carousel-item a {
    display: block;
    width: inherit;
    height: inherit;
    text-indent: -9999px;
    background-color: rgba(var(--carousel-item-empty-color-rgb), 0.5);
    background-image: var(--_image-url);
    background-repeat: no-repeat;
    background-position: center;
    background-size: cover;
    transition: filter var(--carousel-transition-duration) var(--carousel-transition-ease);
    filter: grayscale(100%);
}

.carousel .carousel-item:hover a {
    filter: grayscale(0%);
}

.carousel .carousel-item::before {
    content: '';
    width: inherit;
    height: inherit;
    background-color: rgba(var(--carousel-item-empty-color-rgb), 0.5);
    background-image:
        linear-gradient(to top, rgba(var(--carousel-bg-color-rgb), 0.25) 0%, rgba(var(--carousel-bg-color-rgb), 1.0) 75%),
        var(--_image-url);
    background-repeat: no-repeat;
    background-position: center;
    background-size: cover;
    pointer-events: none;
    filter: blur(var(--carousel-item-reflection-blur)) grayscale(100%);
    transition: filter var(--carousel-transition-duration) var(--carousel-transition-ease);
    transform-style: inherit;
    transform-origin: center bottom;
    transform: rotateX(90deg) rotateZ(180deg) rotateY(180deg);
    position: absolute;
}

.carousel .carousel-item:hover::before {
    filter: blur(var(--carousel-item-reflection-blur)) grayscale(0%);
}

.carousel .carousel-ground {
    --_width: var(--_diameter);
    --_height: var(--_diameter);
    --_rotation: 90deg;
    left: calc(var(--_radius) - var(--_width) / 2);
    top: calc(var(--_radius) - var(--_height) / 2);
    transform: rotateX(var(--_rotation)) translateZ(calc(var(--_item-height) / -2));
    width: var(--_width);
    height: var(--_height);
    border-radius: 50%;
    background: radial-gradient(rgba(var(--carousel-shadow-color-rgb), 0.75) 15% , rgba(var(--carousel-bg-color-rgb), 0) 60%);
    opacity: 0.5;
    transition: opacity var(--carousel-transition-duration) var(--carousel-transition-ease);
    position: absolute;
}

.carousel .carousel-item-wrapper:has(.carousel-item:hover) .carousel-ground {
    opacity: 0.75;
}

/*
Author badge
Small signature link back to niklasknaack.de.
Not part of the actual experiment.
*/
.nk {
    --_size: 48px;
    --_padding: 16px;
    --_blur-filter: 3px;
    --_color-bg-start: rgba(255,255,255,0.55);
    --_color-bg-end: rgba(255,255,255,0.80);
    --_color-bg: var(--_color-bg-start);
    --_color-logo-start: rgba(0,0,0,0.55);
    --_color-logo-end: rgba(0,0,0,1.00);
    --_color-logo: var(--_color-logo-start);
    --_logo-url: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 251 140'%3E%3Cpath fill='black' d='M 97.35 70 L 95.7 67.8 Q 95.421875 67.47421875 95.15 67.1 94.7875 66.66484375 94.4 66.2 92.9564453125 64.3546875 91.5 62.5 L 70 35.1 69.95 35 42.55 0 0 0 0 140 42.55 140 42.55 62.5 42.6 62.5 103.25 140 152.35 140 140 124.25 139.95 124.15 Q 136.15 119.4 132.4 114.6 131.45 113.4 130.55 112.2 129.8 111.3 129.15 110.4 L 97.55 70 152.35 0 97.35 0 97.35 70 M 201.3 0 L 198.05 4.2 Q 197.65 4.65 197.3 5.15 L 195 8.1 195 7.95 170.75 39.15 170.7 39.1 170.6 39.25 146.6 70 146.65 70.05 158.25 84.9 Q 163.1 91.15 168.05 97.4 168.3 97.75 168.6 98.15 168.8 98.4 169 98.7 L 170.25 100.3 170.6 100.85 170.7 100.95 170.75 100.9 171.6 102 Q 171.75 102.15 171.9 102.35 172.05 102.6 172.25 102.85 173 103.8 173.8 104.8 L 201.2 140 250.8 140 203.2 80.25 Q 202.95 79.95 202.75 79.7 L 201.3 77.95 201.3 77.85 195.1 70.05 195.1 70 250.75 0 201.3 0 Z'/%3E%3C/svg%3E");
    --_logo-size: 56%;
    position: fixed;
    right: var(--_padding);
    bottom: var(--_padding);
    z-index: 9999;
    display: block;
    width: var(--_size);
    aspect-ratio: 1;
    border-radius: 50%;
}

.nk:before,
.nk:after {
    content: '';
    position: absolute;
    transition: background-color 250ms ease-in-out;
}
.nk:before {
    inset: 0;
    background-color: var(--_color-bg);
    border-radius: inherit;
    backdrop-filter: blur(var(--_blur-filter));
    -webkit-backdrop-filter: blur(var(--_blur-filter));
    mask:
        linear-gradient(#000 0 0),
        var(--_logo-url) center / var(--_logo-size) auto no-repeat;
    -webkit-mask:
        linear-gradient(#000 0 0),
        var(--_logo-url) center / var(--_logo-size) auto no-repeat;
    mask-composite: exclude;
    -webkit-mask-composite: xor;
}
.nk:after {
    inset: calc((100% - var(--_logo-size)) * .5);
    background-color: var(--_color-logo);
    mask: var(--_logo-url) center / contain no-repeat;
    -webkit-mask: var(--_logo-url) center / contain no-repeat;
}

.nk:hover {
    --_color-bg: var(--_color-bg-end);
    --_color-logo: var(--_color-logo-end);
}