XF 2.3 alternative color code

[webtiryaki]

2.3.0 Beta 3

Hello, what am I doing wrong in the code below? System is not working, Dark is not working.

:root {
  --my-gradient: linear-gradient(135deg, #2d3393, #22bcdc); /* define gradient variable */
}
@media (prefers-color-scheme: dark) {
:root {
     --my-gradient: linear-gradient(135deg, #1B2129, #1B2129);
 }
}

html[data-variation="alternate"] {
:root {
     --my-gradient: linear-gradient(135deg, #1B2129, #1B2129);
 }
}
.p-pageWrapper {
    z-index: 0;
}
.p-pageWrapper:before {
    content: '';
    position: fixed;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    background-image: var(--my-gradient);
    background-size: cover;
    z-index: -1;
}