javascript value to css

element.style.width = '50px';

Where element is a reference to the element.

You can not manipulate external file via javascript. If your class is located in an external css file then you can not change that. What all developers do is changing classes that located in current html file or changing style attribute

if you want to change the css styleSheet rules for all elements, you can do that with simple javascript:

function findCssRule(cssSelectorName)    
{
     var stylesheets  = document.styleSheets;
     for(var i = 0, ii = stylesheets.length;i<ii;i++)
     {
         for(var j = 0, jj = stylesheets[i].rules.length;j<jj;j++)
         { 
             if(stylesheets[i].rules[j].selectorText == cssSelectorName)
             {
                 return stylesheets[i].rules[j];
             }
         }
     }
     return null;
}

//set the width to 80px for '.carpe_slider_slitss' css rule
var cssRule = findCssRule('.carpe_slider_slitss');
if(cssRule!=null)
    cssRule.style.width = '80px';

this is a way to do it

    //ether create a new style sheet
var style = document.createElement ("style");
document.getElementByTagName('head')[0].appendChild(style);
    //or find a document you want to edit
    //ether local
var style = document.getElementByTagName('style')[0];
    //or imported
var style = document.getElementByTagName('style')[0];

style = style.sheet ? style.sheet : style.styleSheet;
if(style.insertRule){
         //insertRule('your css code',new rule index);
    style.insertRule('carpe_slider_slitss{ width: 50px; }', style.cssRules.length); //You can use 0 to insert your rule at the start of the style
}else{   //this is the ie < 9 way
    style.addRule('carpe_slider_slitss', 'width: 50px', style.cssRules.length);
}