Enhance imperial measurement converter layout and features

Added Bootstrap stylesheet link and improved dropdown functionality.

Author: cuthbert86

imperial_measurement_system.html

@@ -6,7 +6,7 @@
     <meta name="viewport" content="width=device-width, initial-scale=1">
     <link rel="stylesheet" href="https://github.com/cuthbert86/cuthbert86.github.io/blob/main/bootstrap.css">
     <link rel="stylesheet" href="https://github.com/cuthbert86/cuthbert86.github.io/blob/main/styles.css">
-
+    <link rel="stylesheet" href="bootstrap.css">
     <style>
         body {
             background: #e6e5e5;