Here's my step in Ubuntu 16.04 and Tomcat 8.
Copy folder /var/lib/tomcat8/webapps/ROOT to your folder.
cp -r /var/lib/tomcat8/webapps/ROOT /var/lib/tomcat8/webapps/{yourfolder}
Add your html, css, js, to your folder.
Open "http://localhost:8080/{yourfolder}" in browser
Notes:
If you using chrome web browser and did wrong folder before, then clean web browser's cache(or change another name) otherwise (sometimes) it always 404.
The folder META-INF with context.xml is needed.