If something or someone is downhill, they are located down a slope or are heading in the direction of the bottom of a hill.
downhill ski runs.
向下的滑雪坡道。
If you say that a task or situation is downhill after a particular stage or time, you mean that it is easy to deal with after that stage or time.
Well, I guess it's all downhill from here.
好,我想从现在起该一帆风顺了。
If something or someone is moving downhill or is downhill, they are moving down a slope or are located towards the bottom of a hill.
He headed downhill towards the river.
他朝山脚下的小河走去。
If you say that something is going downhill, you mean that it is becoming worse or less successful.
Since I started to work longer hours things have gone steadily downhill.
自从我延长了工作时间以后,情况不断恶化。