网页步骤

去除外边距

body,div,dl,dt,dd,ul,ol,li,h1,h2,h3,h4,h5,h6,pre,code,form,fieldset,lege
nd,input,textarea,p,blockquote,th,td,hr,button,article,aside,details,figc
aption,figure,footer,header,hgroup,menu,nav,section {
    margin:0;
    padding:0;
}