用法：
//使用颜色作为背景
s pressed = "#333333"
s selected = "#333333"
s normal = "#888888"
s b = nuibs(pressed, selected, normal)

//使用图像作为背景
s pressed = "%a.png"
s selected = "%a.png"
s normal = "%b.png"
s b = nuibs(pressed, selected, normal)

//使用渐变颜色作为背景
.配置选中状态背景
s a = 0
s b = 0
s c = "#255779|#3e7492|#a6c0cd"
s d = "0"
s e = "topbottom"
s pressed = ngde(a, b, c, d, e)

.配置正常状态背景
s a = 0
s b = 0
s c = "#255779|#3e7492|#a6c0cd"
s d = "0"
s e = "rightleft"
s normal = ngde(a, b, c, d, e)

s selected = pressed

s b = nuibs(pressed, selected, normal)

说明：
输入按下背景，输入选中背景，正常状态背景。