float://浮动
width: //宽度
_height//高度:
min-height: //最小高度，会根据内容自动增长
font-size: 18px//字体大小
font-family: "微软雅黑"//字体
top: 20px据顶部20px
padding-left: 35px//外边距左35px
color: #b60303//颜色值
letter-spacing: 3px//每个字母相隔距离
padding//外边距
line-height: 20px行高
margin: 0px auto
padding: 0px
text-decoration: none//无下划线
text-decoration: underline有下划线
text-align: center居中
padding-top: 9px外边距顶部9px
cursor: pointer//把你的光标放到相应文字上查看效果
要注意光标的实际效果依赖于用户的系统设置，与你在这里看到的效果并不一定一致。
cursor: crosshair
十字准心
The cursor render as a crosshair
游标表现为十字准线
cursor: pointer
cursor: hand
写两个是为了照顾IE5，它只认hand。
手
The cursor render as a pointer (a hand) that indicates a link
游标以暗示(手指)的形式来表明有一个连接
cursor: wait
等待/沙漏
The cursor indicates that the program is busy (often a watch or an hourglass)
游标暗示当前程序正忙(一般为一块表或是一个沙漏)
cursor: help
帮助
The cursor indicates that help is available (often a question mark or a balloon)
游标暗示当前位置可得到帮助(一般为问号或是气球)
cursor: no-drop
无法释放
cursor: no-drop
cursor: text
文字/编辑
The cursor indicates text
游标暗示当前所处位置为文字内容
cursor: move
可移动对象
The cursor indicates something that should be moved
游标暗示一些东西应该被移动
cursor: n-resize
向上改变大小(North)
The cursor indicates that an edge of a box is to be moved up (north)
边缘可向上移动(北)
cursor: s-resize
向下改变大小(South)
The cursor indicates that an edge of a box is to be moved down (south)
边缘可向下方移动(南)
cursor: e-resize
向右改变大小(East)
The cursor indicates that an edge of a box is to be moved right (east)
box边缘可向右(东)边移动
cursor: w-resize
向左改变大小(West)
The cursor indicates that an edge of a box is to be moved left (west)
边缘可向左移动(西)
cursor: ne-resize
向上右改变大小(North East)
The cursor indicates that an edge of a box is to be moved up and right (north/east)
游标暗示box的边缘可向右上方移动(东北方向)
cursor: nw-resize
向上左改变大小(North West)
The cursor indicates that an edge of a box is to be moved up and left (north/west)
边缘可向左上方移动(西北)
cursor: se-resize
向下右改变大小(South East)
The cursor indicates that an edge of a box is to be moved down and right (south/east)
边缘可向右下方移动(东南)
cursor: sw-resize
向下左改变大小(South West)
The cursor indicates that an edge of a box is to be moved down and left (south/west)
边缘可向左下方移动(西南)
cursor: auto
自动
The browser sets a cursor
浏览器设置一个游标
cursor:not-allowed
禁止
cursor:not-allowed
cursor: progress
处理中
cursor: progress
cursor: default
系统默认
The default cursor (often an arrow)
默认的游标状态（通常为一个箭头）
cursor: url(' # ')
# = 光标文件地址 (注意文件格式必须为：.cur 或 .ani)。
用户自定义（可用动画）
The url of a custom cursor to be used.
自定义游标的url位置
Note: Always define a generic cursor at the end of the list in case none of the url-defined cursors can be used
注意：在定义完自定义的游标之后在末尾加上一般性的游标，以防那些url所定义的游标不能使用
浮力原理!大气是介质，随着高度上升，虽然大气密度减小，但是气球体积变大，因此浮力变大，当到达某一高度区域时，浮力等于气球重力!在某一固定高度大气密度也是有微小变化，所以浮力也有变化，因而气球上下浮动！气球飘浮的原理： 气球受自身的重力和空气浮力。自身重力=气球重力+球内氢气重力
空气浮力=空气平均密度*g*气球体积
根据牛顿第二定律：
空气浮力-自身重力=ma>0
