@layer properties {
  @property --bg-position {
    syntax: "<number>";
    inherits: true;
    initial-value: 100;
  }
  @property --after-blur {
    syntax: "<number>";
    inherits: true;
    initial-value: 0;
  }
  @property --after-opacity {
    syntax: "<number>";
    inherits: true;
    initial-value: 1;
  }
  @property --before-opacity {
    syntax: "<number>";
    inherits: true;
    initial-value: 0.3;
  }
  @property --btn-offset {
    syntax: "<number>";
    inherits: true;
    initial-value: 1;
  }
  @property --btn-scale {
    syntax: "<number>";
    inherits: true;
    initial-value: 1;
  }
}

:root {
  --debug: 0;

  /* colors */
  --body-bg: hsl(0, 0%, 6%);
  --btn-bg: hsl(0, 0%, 0%);
  --btn-border-width: 1.5;
  --btn-offset: 1;
  --btn-scale: 1;
  --after-bg: linear-gradient(
    to right,
    rgb(0 0 0),
    rgb(0 0 0),
    rgb(0 0 0),
    rgb(0 0 0),
    rgb(0 0 0),
    rgb(0 0 0),
    rgb(0 0 0),
    rgb(0 0 0),
    rgb(0 0 0),
    rgb(0 0 0),
    rgb(0 0 0),
    rgb(0 0 0),
    rgb(0 0 0)
  );
  --after-blur: 10;
  --after-opacity: 1;
  --after-pos-y: 10;
  
  --before-opacity: 0.3;

  /* positions */
  --bg-position: 100;

  --color-white: hsl(0, 0%, 100%);
  --color-cyan: hsl(180, 100%, 50%);
  --color-blue: hsl(240, 100%, 50%);
  --color-purple: hsl(270, 100%, 50%);
  --color-pink: hsl(330, 40%, 70%);
  --color-red: hsl(0, 100%, 50%);
  --color-yellow: hsl(60, 100%, 50%);
  --color-lime: hsl(90, 100%, 75%);

  --color-orange: oklch(69.1% 0.223 36.85);
}

@supports (color: color(display-p3 0 0 0)) {
  :root {
    --color-white: color(display-p3 1 1 1);
    --color-cyan: color(display-p3 0 1 1);
    --color-blue: color(display-p3 0 0 1);
    --color-purple: color(display-p3 0.5 0 1);
    --color-pink: color(display-p3 1 0.4 0.7);
    --color-red: color(display-p3 1 0 0);
    --color-yellow: color(display-p3 1 1 0);
    --color-lime: color(display-p3 0.75 1 0);

    --color-orange: color(display-p3 0.96 0.39 0.2);
  }
}

*,
*:before,
*:after {
  box-sizing: border-box;
  outline: calc(var(--debug) * 1px) dotted red;
  outline-offset: -1px;
}

main {
  width: 100%;
  height: 50%;
  padding: 0;
  margin: 0;
}

body {
  /* background: var(--body-bg); */
  font-family: "WIN", sans-serif;
}

main {
  display: grid;
  place-items: center;

  & button {
    all: unset;
    background: transparent;
    border-width: 0;
    transform: scale(var(--btn-scale));
    transition: 
        --bg-position 3s ease, 
        --after-blur 0.3s ease,
        --before-opacity 0.3s ease,
        --btn-offset 0.3s ease,
        --btn-scale 0.2s cubic-bezier(.76,-0.25,.51,1.13);

    > div {
      display: block;
      padding: 0.8em 1.2em;
      background: var(--btn-bg);
      color: white;
      font-weight: bold;
      border-radius: 8px;
      font-size: 22px;
      position: relative;
      
      cursor: pointer;

      &:not(:hover) {
        transition: --after-blur 0.3s ease;
      }

      > span {
        background: linear-gradient(
            to right,
            var(--color-white),
            var(--color-white),
            var(--color-cyan),
            var(--color-blue),
            var(--color-purple),
            var(--color-pink),
            var(--color-red),
            var(--color-yellow),
            var(--color-lime),
            var(--color-white),
            var(--color-white)
          )
          no-repeat calc(var(--bg-position) * 1%) 0% / 900%;
        -webkit-background-clip: text;
        -webkit-text-fill-color: transparent;
        letter-spacing: 0.15ch;
        font-weight: 600;
      }

      &:after {
        display: block;
        position: absolute;
        content: "";
        width: 100%;
        height: 100%;
        background: var(--after-bg) no-repeat calc(var(--bg-position) * 1%) 0% /
          900%;
        transform: translateY(calc(var(--after-pos-y) * 1px));
        left: 0;
        top: 0;
        z-index: -2;
        filter: blur(calc(var(--after-blur) * 1px));
        opacity: var(--after-opacity);
      }

      &:before {
        content: "";
        display: block;
        position: absolute;
        width: calc(100% + calc(calc(var(--btn-border-width) * 2) * 1px));
        height: calc(100% + calc(calc(var(--btn-border-width) * 2) * 1px));
        background: linear-gradient(
            to right,
            var(--color-white),
            var(--color-white),
            var(--color-cyan),
            var(--color-blue),
            var(--color-purple),
            var(--color-pink),
            var(--color-red),
            var(--color-yellow),
            var(--color-lime),
            var(--color-white),
            var(--color-white)
          )
          no-repeat calc(var(--bg-position) * 1%) 0% / 900%;
        border-radius: 9px;
        z-index: -1;
        top: calc(var(--btn-border-width) * -1px);
        left: calc(var(--btn-border-width) * -1px);
        opacity: var(--before-opacity);
      }
    }

    &:hover {
      --btn-scale: 1.05;
      --bg-position: 0;
      --after-bg: linear-gradient(
          to right,
          var(--color-white),
          var(--color-white),
          var(--color-cyan),
          var(--color-blue),
          var(--color-purple),
          var(--color-pink),
          var(--color-red),
          var(--color-yellow),
          var(--color-lime),
          var(--color-white),
          var(--color-white)
        );
        --after-blur: 30;
        --after-opacity: 0.3;
        --after-pos-y: 0;
        --before-opacity: 1;      
        --btn-offset: 5;
      
      &:active {
        --btn-scale: 0.98;
        --after-blur: 15;
      }
    }
  }
}