Added backgrund built-in component

src/builtin-components/Background/Background.sass

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+@use '/src/styles/classes.sass'

src/builtin-components/Background/Background.tsx

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+import './Background.sass'
+import { Show } from 'solid-js'
+import backgroundAvif from '../../assets/images/background.avif'
+import backgroundWebp from '../../assets/images/background.webp'
+
+interface Props {
+  image?: boolean
+  color?: string
+}
+
+export default (props: Props) => {
+  return (
+    <>
+      <Show when={props.image}>
+        <picture class="fullscreen">
+          <source srcset={backgroundAvif.src} type="image/avif" />
+          <source srcset={backgroundWebp.src} type="image/webp" />
+          <img src={backgroundWebp.src} width="1920" height="auto" decoding="async" loading="lazy" alt="An image background" />
+        </picture>
+      </Show>
+
+      <Show when={!props.image}>
+        <div style={{ background: props.color }} class="fullscreen" />
+      </Show>
+    </>
+  )
+}