First of All Try the Code Below in your .htaccess file -
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteRule ^/SearchResult/$1 SearchResult.php?id=$1 [NC,L]
</IfModule>
The code Above is for SearchResult.php Page For adding more pages you can undrestand and use similar type of code above like for About.php you can use below -
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteRule ^/SearchResult/$1 SearchResult.php?id=$1 [NC,L]
RewriteRule ^/About/$1 About.php [NC,L]
</IfModule>
In You Case your urls will work as you need after above changesin .htaccess file . But your page css is fumbled after this as you js and specially your css files are not having root path try solution below -
Convert following code lines
<link href="css/bootstrap.min.css" rel="stylesheet" async>
<script src="js/jquery.min.js" ></script>
<script src="js/bootstrap.min.js" ></script>
<script src="js/alertify.min.js" type="text/javascript" ></script>
To Below
<link href="/css/bootstrap.min.css" rel="stylesheet" async>
<script src="/js/jquery.min.js" ></script>
<script src="/js/bootstrap.min.js" ></script>
<script src="/js/alertify.min.js" type="text/javascript" ></script>