css positioning_html/css_WEB-ITnose

Hello everyone
The following html code:

I want to realize that mainTool is always at the bottom, and the height of content is other than mainTool. So my css is written like this:

*{margin:0;padding:0;}html,body{    height: 100%;}body{    background: black;}#content {    height:100%;    border-bottom: 50px; }#mainTool  {    position:absolute;   //这里设置绝对定位，当有这一句时，整个mainTool都消失不见了。去掉的话就可以见到。    bottom: 0px;     ／／使它一直在底部    background-color: yellow ;    height: 50px;     ／／高度为固定的50px；}

I don’t know where the css problem is, please help

Reply to the discussion (Solution)

#mainTool  {    position:absolute;    bottom: 0px;    background-color: yellow ;    height: 50px;    width:100%; /*增加这一条样式*/}

That’s it. Thanks. That's it.
CSS code
#mainTool {
position:absolute;
bottom: 0px;
background-color: yellow;
height: 50px;
width:100%; / *Add this style*/
}