Navigate to your httpd.conf file (xamppapacheconf) and open it using your favourite text editor.

If you do not have access to this folder/file, open your .htaccess file instead.

Underneath the "#LoadModule" lines, add the following:

# Instruct the browser to always check for the latest version of your files using Apache directives
<IfModule mod_headers.c>
    <FilesMatch "(?i)^.*.(css|htm|html|gif|jpg|jpeg|js|png|pdf)$">
    Header set Cache-Control "max-age=0,must-revalidate"
    </FilesMatch>
</IfModule>