Edit in JSFiddle

$("#setwidth").click(function () {
    $("body").css("width", "50%");
});
$("#setheight").click(function () {
    $("body").css("height", "4em");
});
$("#sethtmlback").click(function () {
    $("html").css("background", "#333");
});

<button id="setwidth">设置body宽度</button>
<button id="setheight">设置body高度</button>
<button id="sethtmlback">设置html背景</button>

<h1>Lorem ipsum</h1>
<p>Lorem ipsum</p>
<p>Lorem ipsum</p>
<p>Lorem ipsum</p>
<p>Lorem ipsum</p>
<p>Lorem ipsum</p>
<p>Lorem ipsum</p>
<p>Lorem ipsum</p>
<p>Lorem ipsum</p>
<p>Lorem ipsum</p>
<p>Lorem ipsum</p>

body {
    border: 1px solid;
    background-image: url("data:image/svg+xml;base64,PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0iVVRGLTgiIHN0YW5kYWxvbmU9Im5vIj8+CjxzdmcgeG1sbnM9Imh0dHA6Ly93d3cudzMub3JnLzIwMDAvc3ZnIiBoZWlnaHQ9IjEyOCIgd2lkdGg9IjEyOCI+CiAgPGNpcmNsZSBjeD0iNjQiIGN5PSI2NCIgcj0iNjQiIGZpbGw9InJlZCIvPgo8L3N2Zz4K");
    background-repeat: no-repeat;
    background-position: bottom right;
}