css

1. 查看页面布局

(function(){

            var style = document.querySelector('#_outline_');
            if (style) {
                    style.parentNode.removeChild(style);
            } else {
                    style = document.createElement('style');
                    style.id = '_outline_';
                    style.innerHTML = "*{outline: 1px solid red}";
                    document.body.appendChild(style);
            }
        })()