hiding side navigation box on SharePoint root site homepage

hide-side-nav.css

/* only on root site homepage, hide the side nav box */
[data-root-home=true] #sideNavBox {
  display: none !important;
}

sharepoint-home-page-detection.js

// you might want to wait until dom is ready before executing this code
_spPageContextInfo.isWebWelcomePage; // true if homepage of root site or a subsite
_spPageContextInfo.siteServerRelativeUrl === _spPageContextInfo.webServerRelativeUrl; // true means we're on a root site, false on a subsite

// so, we're on a homepage that could be for root site or a subsite
if( _spPageContextInfo.isWebWelcomePage ) {
  if( _spPageContextInfo.siteServerRelativeUrl === _spPageContextInfo.webServerRelativeUrl ) {
    // homepage of a root site
    // add attribute to `html` element, so we can utilize it from css
    document.documentElement.setAttribute('data-root-home', true);
  } else {
    // homepage of a sub site
  }
}