feat(calc-02): add cursor-aware editing in the X stack display

samples/calc-02/index.css

@@ -137,6 +137,10 @@ body {
 	justify-self: end;
 	font-size: 20px;
 }
+
+.stack-value.is-editing {
+	letter-spacing: 0.02em;
+}
 .display-buttons-panel {
 	padding: 8px;
 	min-height: 0;
@@ -379,6 +383,37 @@ button:active {
 	outline-offset: 2px;
 }
 
+.stack-value.is-editing {
+	display: inline-flex;
+	align-items: center;
+	justify-content: flex-end;
+	gap: 0;
+}
+
+.edit-text {
+	display: inline-block;
+	white-space: pre;
+}
+
+.edit-caret {
+	display: inline-block;
+	width: 1px;
+	height: 1em;
+	margin: 0 0.12ch;
+	background: currentColor;
+	animation: caret-blink 1s steps(1, end) infinite;
+	transform: translateY(0.02em);
+}
+
+@keyframes caret-blink {
+	0%, 49% {
+		opacity: 1;
+	}
+	50%, 100% {
+		opacity: 0.15;
+	}
+}
+
 .key-default {
 	background: linear-gradient(180deg, var(--btnTop), var(--btnBottom));
 	color: #eef2f7;