This is the 5142nd most frequent Japanese word.
逆さ
Upside down; inverted.
Here, '逆さ (sakasa)' is used to indicate the state of being inverted or upside-down.
絵が逆さに貼られていました。
The picture was pasted upside-down.
In this context, '逆さ (sakasa)' is used to describe the action of turning something upside-down.
逆さにしても中身が漏れない容器です。
It's a container that doesn't leak even when turned upside-down.
Here, '逆さ (sakasa)' is describing the outcome or observation made when something is upside-down.