Убрал приведение всех нажатых клавиш к маленьким буквам

rollup.config.js

@@ -9,7 +9,7 @@ const production = !process.env.ROLLUP_WATCH;
 export default {
 	input: 'src/main.js',
 	output: {
-		sourcemap: false,
+		sourcemap: !production,
 		format: 'iife',
 		name: 'app',
 		file: 'public/bundle.js'

src/App.svelte

@@ -35,7 +35,7 @@
 	function onKey(event) {
 		const key = event.detail;
 
-		if (key === 'backspace') {
+		if (key.toLowerCase() === 'backspace') {
 			lastKeys = lastKeys.slice(0, -1);
 		} else if (key.length === 1) {
 			lastKeys += key;

src/components/KeyPress.svelte

@@ -4,7 +4,7 @@
 	const dispatch = createEventDispatcher();
 
 	function onKeyDown(event) {
-		dispatch('key', event.key.toLowerCase());
+		dispatch('key', event.key);
 	}
 </script>
 

src/trainings/selectKeys/Setup.svelte

@@ -3,7 +3,7 @@
     import {selectKeys} from './store';
 
 	function onKey(event) {
-		const key = event.detail;
+		const key = event.detail.toLowerCase();
 
 		if (key === 'backspace') {
 			selectKeys.removeLastKey();