//->REM
~function () {
    var desW = 750,
        winW = document.documentElement.clientWidth,
        ratio = winW / desW,
        oMain = document.querySelector('.main');
    if (winW > desW) {
        oMain.style.margin = '0 auto';
        oMain.style.width = desW + 'px';
        return;
    }
    document.documentElement.style.fontSize = ratio * 100 + 'px';
}();