Update README.md

Author: Parth2753

README.md

@@ -28,7 +28,42 @@ The Calculator have features are as follows:
 # Usage
 Compile and run it
 <br>
-========> javac Calculator.java
+<!-- GitHub-style code block with Copy button -->
+<div style="
+  position: relative;
+  background-color: #1e1e1e;
+  border-radius: 8px;
+  padding: 1rem 1.2rem;
+  font-family: 'Courier New', monospace;
+  color: #e6edf3;
+  line-height: 1.5;
+  overflow-x: auto;
+  box-shadow: 0 2px 6px rgba(0,0,0,0.3);
+">
+  <button
+    onclick="navigator.clipboard.writeText('javac Calculator.java\njava Calculator')"
+    style="
+      position: absolute;
+      top: 8px;
+      right: 8px;
+      background: #2d2d2d;
+      color: #e6edf3;
+      border: 1px solid #444c56;
+      border-radius: 6px;
+      padding: 4px 8px;
+      font-size: 12px;
+      cursor: pointer;
+      transition: background 0.2s;
+    "
+    onmouseover="this.style.background='#3a3a3a'"
+    onmouseout="this.style.background='#2d2d2d'"
+  >
+    Copy code
+  </button>
+
+  <pre style="margin: 0;"><code style="color: #79c0ff;">javac</code> Calculator.java
+<code style="color: #79c0ff;">java</code> Calculator</pre>
+</div>
 <br>
 Follow the menu options in the calculator.