getStyleValue.js

function getStyle(selector){

  var styles = document.styleSheets;
  var sheets = Array.from(styles);
  var data, element, tot = sheets.length;
  
  for(var i = 0; i < tot; i++) {
    
    element = sheets[i];
    
    if(element.cssRules) {
      
      var tmp = Array.from(element.cssRules);
      var filtered = tmp.filter(el => {
          return el.selectorText && el.selectorText.indexOf(selector) >= 0
          });
      
      if(filtered && filtered.length){
        
        data = filtered;
        break;
        
      }
    }
    
  }

  return data;

}

function getStyleValue(rule, property) {

	var found = [],         
      regex = /{([^}]+)}/g,
      curMatch,
      tot;

      while( curMatch = regex.exec( rule.cssText ) ) {
        found.push(curMatch[1].trim());
      }

	var values = found.filter(element => element.indexOf(property) >= 0),
        tot = values.length,
        val;
    
     for (var i = 0; i < tot; i++){
       
       val = values[i].split(':')[1];
       found = [],          
       regex = /"([^}]+)"/g,
       curMatch;   
        
       while( curMatch = regex.exec( val ) ) {
        found.push(curMatch[1].trim());
       }  
       return found[0];
    }

}