Update index.html

index.html

@@ -155,7 +155,7 @@ <h3 class="mb-4 text-center">Select A Value To Convert</h3>
         </select>        
 
         <input type="number" class="form-control mb-3" id="valueInputImperial" placeholder="Enter value" value="0">
-        <button class="btn btn-primary mx-auto mb-3" onclick="convertImperial()">Convert</button>
+        <button class="btn btn-primary d-block mx-auto mb-3" onclick="convertImperial()">Convert</button>
         <div class="card" id="resultCardImperial" style="display:none;">
             <div class="card-body bg-primary text-white text-center">
                 <h5 class="card-title">Result</h5>