如何使用javascript从下拉列表更改网页的背景颜色需要这个

I need help regarding JavaScript function code where I want to change the background-color of a web page from drop down list. When someone select any color from the list then it responds as same and change the background color of web page. I used the technique in JS is DOM. How we can done this. Here is my code for this task:-I need help regarding JavaScript function code