createStyle.js

function createStyle(data, useImportant, w) {
    var styleElement, styleContent, selector, property, value;
    w = w || window;
		
    styleContent = '';
    for (selector in data) {
        if (!data.hasOwnProperty(selector)) continue;
        styleContent += '\n' + selector + ' {\n';
        for (property in data[selector]) {
            if (!data[selector].hasOwnProperty(property)) continue;
            value = data[selector][property];
            styleContent += '   ' + property + ': ' + value;
            if (useImportant) {
                styleContent += ' !important';
            }
            styleContent += ';\n'
        }
        styleContent += ' }\n';
    }

    styleElement = w.document.createElement('style');
    styleElement.textContent = styleContent;
    w.document.querySelector('head').appendChild(styleElement);
}