perf: apply preflight vars to :root unocss/unocss#1205

src/preflights.ts

@@ -10,7 +10,7 @@ export const preflights: Preflight[] = [
     getCSS(ctx: PreflightContext<Theme>) {
       if (ctx.theme.preflightBase) {
         const css = entriesToCss(Object.entries(ctx.theme.preflightBase))
-        return `*,::before,::after{${css}}::backdrop{${css}}`
+        return `:root{${css}}`
       }
     },
   },

test/__snapshots__/preset-mini.test.ts.snap

@@ -9,7 +9,7 @@ exports[`preset-mini > custom var prefix 1`] = `
 
 exports[`preset-mini > targets 1`] = `
 "/* layer: preflights */
-*,::before,::after{--un-rotate:0;--un-rotate-x:0;--un-rotate-y:0;--un-rotate-z:0;--un-scale-x:1;--un-scale-y:1;--un-scale-z:1;--un-skew-x:0;--un-skew-y:0;--un-translate-x:0;--un-translate-y:0;--un-translate-z:0;--un-ring-offset-shadow:0 0 #0000;--un-ring-shadow:0 0 #0000;--un-shadow-inset:var(--un-empty,/*!*/ /*!*/);--un-shadow:0 0 #0000;--un-ring-inset:var(--un-empty,/*!*/ /*!*/);--un-ring-offset-width:0px;--un-ring-offset-color:#fff;--un-ring-width:0px;--un-ring-color:rgba(147,197,253,0.5);}::backdrop{--un-rotate:0;--un-rotate-x:0;--un-rotate-y:0;--un-rotate-z:0;--un-scale-x:1;--un-scale-y:1;--un-scale-z:1;--un-skew-x:0;--un-skew-y:0;--un-translate-x:0;--un-translate-y:0;--un-translate-z:0;--un-ring-offset-shadow:0 0 #0000;--un-ring-shadow:0 0 #0000;--un-shadow-inset:var(--un-empty,/*!*/ /*!*/);--un-shadow:0 0 #0000;--un-ring-inset:var(--un-empty,/*!*/ /*!*/);--un-ring-offset-width:0px;--un-ring-offset-color:#fff;--un-ring-width:0px;--un-ring-color:rgba(147,197,253,0.5);}
+:root{--un-rotate:0;--un-rotate-x:0;--un-rotate-y:0;--un-rotate-z:0;--un-scale-x:1;--un-scale-y:1;--un-scale-z:1;--un-skew-x:0;--un-skew-y:0;--un-translate-x:0;--un-translate-y:0;--un-translate-z:0;--un-ring-offset-shadow:0 0 #0000;--un-ring-shadow:0 0 #0000;--un-shadow-inset:var(--un-empty,/*!*/ /*!*/);--un-shadow:0 0 #0000;--un-ring-inset:var(--un-empty,/*!*/ /*!*/);--un-ring-offset-width:0px;--un-ring-offset-color:#fff;--un-ring-width:0px;--un-ring-color:rgba(147,197,253,0.5);}
 /* layer: 1 */
 .uno-layer-1\\\\:translate-0{--un-translate-x:0rpx;--un-translate-y:0rpx;transform:translateX(var(--un-translate-x)) translateY(var(--un-translate-y)) translateZ(var(--un-translate-z)) rotate(var(--un-rotate)) rotateX(var(--un-rotate-x)) rotateY(var(--un-rotate-y)) rotateZ(var(--un-rotate-z)) skewX(var(--un-skew-x)) skewY(var(--un-skew-y)) scaleX(var(--un-scale-x)) scaleY(var(--un-scale-y)) scaleZ(var(--un-scale-z));}
 /* layer: default */