html body {
    background-attachment: fixed;
}

body,
textarea,
input,
select,
button {
    font-size: calc(12px*var(--width));
    font-family: Helvetica, Arial;
}

/*(1)清除默认样式*/
html,
body,
ul,
li,
ol,
dl,
dd,
dt,
p,
h1,
h2,
h3,
h4,
h5,
h6,
form,
fieldset,
legend,
img,
input {
    margin: 0;
    padding: 0;
}

fieldset,
img,
input,
button {
    border: 0 none;
    padding: 0;
    margin: 0;
    outline-style: none;
}

img {
    max-width: 100%;
}

.img100 {
    width: 100%;
    display: block;
}

/* 上下居中 */
.middle {
    -webkit-transform: translate(0, -50%);
    -ms-transform: translate(0, -50%);
    transform: translate(0, -50%);
    position: absolute;
    top: 50%;
}

/* 左右居中 */
.center {
    -webkit-transform: translate(-50%, 0);
    -ms-transform: translate(-50%, 0);
    transform: translate(-50%, 0);
    position: absolute;
    left: 50%;
}

:root {
    --width: 0;
}

/* 上下左右居中 */
.middcent {
    -webkit-transform: translate(-50%, -50%);
    -ms-transform: translate(-50%, -50%);
    transform: translate(-50%, -50%);
    position: absolute;
    left: 50%;
    top: 50%;
}