diff --git a/src/index.html b/src/index.html
index c6db5fc..5e5a1e9 100644
--- a/src/index.html
+++ b/src/index.html
@@ -1,49 +1,53 @@
 <!DOCTYPE html>
 <html lang="en">
-
-<head>
-  <meta charset="UTF-8" />
-  <link rel="icon" type="image/svg+xml" href="/images/favicon.svg" />
-  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
-  <title>calculator</title>
-</head>
-
-<body>
-
-  <main class="wrapper">
-
-    <div class="calculator">
-      <input type="text" class="calculator-input" disabled>
-      <div class="calculator-keys">
-        <button type="button" class="clear active" value="clear">C</button>
-        <button type="button" class="operator active" value="/">&divide;</button>
-        <button type="button" class="operator active" value="*">&times;</button>
-        <button type="button" class="operator operator-on active" value="on-off"></button>
-
-        <button type="button" class="active" value="7">7</button>
-        <button type="button" class="active" value="8">8</button>
-        <button type="button" class="active" value="9">9</button>
-        <button type="button" class="operator active" value="-">-</button>
-
-        <button type='button' class="active" value="4">4</button>
-        <button type="button" class="active" value="5">5</button>
-        <button type="button" class="active" value="6">6</button>
-        <button type="button" class="operator active" value="+">+</button>
-
-        <button type="button" class="active" value="1">1</button>
-        <button type="button" class="active" value="2">2</button>
-        <button type="button" class="active" value="3">3</button>
-        <button type="button" class="equal-sign operator active" value="=">=</button>
-
-        <button type="button" class="zero active" value="0">0</button>
-        <button type="button" class="decimal active" value=".">.</button>
+  <head>
+    <meta charset="UTF-8" />
+    <link rel="icon" type="image/svg+xml" href="/images/favicon.svg" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <title>calculator</title>
+  </head>
+
+  <body>
+    <main class="wrapper">
+      <div class="calculator">
+        <input type="text" class="calculator-input" disabled />
+        <div class="calculator-keys">
+          <button type="button" class="clear active" value="clear">C</button>
+          <button type="button" class="operator active" value="/">
+            &divide;
+          </button>
+          <button type="button" class="operator active" value="*">
+            &times;
+          </button>
+          <button
+            type="button"
+            class="operator operator-on active"
+            value="on-off"
+          ></button>
+
+          <button type="button" class="active" value="7">7</button>
+          <button type="button" class="active" value="8">8</button>
+          <button type="button" class="active" value="9">9</button>
+          <button type="button" class="operator active" value="-">-</button>
+
+          <button type="button" class="active" value="4">4</button>
+          <button type="button" class="active" value="5">5</button>
+          <button type="button" class="active" value="6">6</button>
+          <button type="button" class="operator active" value="+">+</button>
+
+          <button type="button" class="active" value="1">1</button>
+          <button type="button" class="active" value="2">2</button>
+          <button type="button" class="active" value="3">3</button>
+          <button type="button" class="equal-sign operator active" value="=">
+            =
+          </button>
+
+          <button type="button" class="zero active" value="0">0</button>
+          <button type="button" class="decimal active" value=".">?</button>
+        </div>
       </div>
-    </div>
-
-  </main>
-
-
-  <script type="module" src="js/app.js"></script>
-</body>
+    </main>
 
-</html>
\ No newline at end of file
+    <script type="module" src="js/app.js"></script>
+  </body>
+</html>
