//Pictures
 <picture>
       <source
    media="(max-width:599px) and (prefers-color-scheme: light)"
    srcset="images/bg-mobile-light.jpg"
    />
      <source
    media="(max-width:599px) and (prefers-color-scheme: dark)"
    srcset="images/bg-mobile-dark.jpg"
    />
      <source
    media="(min-width:600px) and (prefers-color-scheme: light)"
    srcset="images/bg-desktop-light.jpg"
    />
      <source
    media="(min-width:600px) and (prefers-color-scheme: dark)"
    srcset="images/bg-desktop-dark.jpg"
    />
      <img
    src="images/bg-mobile-light.jpg"
    aria-hidden="true"
    class="background-img"
    alt=""
    />
</picture>
 
//CSS
@media (prefers-color-scheme: dark) {
  :root {
    --color-primary: #25273c;
    --color-primary-text: #e4e5f1;
    --color-secondary-text: #cacde8;
    --color-deleted-text: #4d5067;
    --color-circle: #777a92;
    --color-background: #161722;
    --color-background-hover: #1c1e35;
  }
}
 
@media (prefers-color-scheme: light) {
  :root {
    --color-white: #ffffff;
    --color-primary: #ffffff;
    --color-primary-text: #494c6b;
    --color-secondary-text: #9394a5;
    --color-light-text: #d4d4d4;
    --color-active: #3a7cfd;
    --color-circle: #d6d6d6;
    --color-background: #fafafa;
    --color-background-hover: #ebebeb;
    --color-background-modal: rgba(73, 76, 107, 0.6);
    --color-error: #cd1237;
  }
}
 
 
//JS
let dark = window.matchMedia('(prefers-color-scheme: dark)').matches;
//Show which prefers-color-scheme user has before the page loads
window.matchMedia('(prefers-color-scheme: dark)');
if (dark) {
  //Do something
} else {
  //Do something
}