CSS 练习:

将以下 5 个步骤添加到动画“示例”中 （使用 0%、25%、50%、 75% 和 100%）：

1. 0% - Set background color to "red", left position to "0px", top position to: "0px"
2. 25% - Set background color to "blue", left position to "0px", top position to: "200px"
3. 50% - Set background color to "green", left position to "200px", top position to: "200px"
4. 75% - Set background color to "yellow", left position to "200px", top position to: "0px"
5. 100% - Set background color to "red", left position to "0px", top position to: "0px"

Hint: The % values represents the different stages of the animation. 0% is the start, and 100% is the end.