Maybe it could refer to either the poet or the sun throughout the entire line, if you think of the mantle blue as being the actual sky that the sun is able to twitch over his shoulder.

或者两者皆可,从整句的行文看来，如果你们把蓝色的丝巾看作是真实的天空的话,那么太阳的确是能够在他的肩上轻轻颤动。

耶鲁公开课 - 弥尔顿课程节选

It's too loud. I mean even if you banged on it lightly, it would be too loud

这声音太大了。就算是你轻轻地敲，发出的声音也不算小。

Would you please 实战 - SpeakingMax英语口语达人

If the person next to you is asleep, gently wake him or her up.

如果你身边的人睡着了，轻轻地把他或她唤醒。

哈佛公开课 - 幸福课课程节选

First he was touched and now he touches.

开始时他被轻轻的触动，后来他开始触动别人。

耶鲁公开课 - 弥尔顿课程节选

Don't you want to just reach out and pinch it? It's so cute.

你难道不想伸出手轻轻捏一下吗？实在太可爱了。

so that 实战 - SpeakingMax英语口语达人

And then, the first kiss.

然后，轻轻的一个初吻。

It's like 实战 - SpeakingMax英语口语达人