Import style using <link> tag and replace {DOMAIN} with the current domain:
HTML
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no" />
<link rel="stylesheet" href="{DOMAIN}/tikui.css" />
<link rel="stylesheet" href="{DOMAIN}/montserrat/index.css" />
<link rel="stylesheet" href="{DOMAIN}/montserrat/700.css" />
Pug
meta(name='viewport' content='width=device-width, initial-scale=1, shrink-to-fit=no')
link(rel='stylesheet' href='{DOMAIN}/tikui.css')
link(href='{DOMAIN}/montserrat/index.css' rel='stylesheet')
link(href='{DOMAIN}/montserrat/700.css' rel='stylesheet')
The Style have an Atomic Design structure: