update selection styling to use css variable (#10437)

app/src/interfaces/input-rich-text-html/get-editor-styles.ts

@@ -23,6 +23,9 @@ export default function getEditorStyles(font: 'sans-serif' | 'serif' | 'monospac
 	url(${merriweatherRegular}) format('woff');
 }
 
+::selection {
+	background: ${cssVar('--background-normal-alt')};
+}
 body {
 	color: ${cssVar('--foreground-normal')};
 	background-color: ${cssVar('--background-input')};

app/src/styles/_base.scss

@@ -108,7 +108,7 @@ strong {
 }
 
 ::selection {
-	background: #e1f0fa;
+	background: var('--background-normal-alt');
 }
 
 dl > div {