请考虑使用FractionallySizedBox来设置应从所有屏幕获取的宽度/高度的百分比：

FractionallySizedBox(
  heightFactor: 0.2, // will take 20% of the screen height.
  widthFactor: 0.4, // will take 40% of the screen width.
);

If you want to create a condition for each screen size but avoid messy code. You should try to do it with an extension.
For example:

extension BoxWithSizes on double {
   
   double get conditional {
        return (//size of screen < 600) ? this : this - 30;
   }

}

And use it like

SizedBox(width: 30.conditional)

The thing with this is that you should do like in CSS, a different getter extension for differents components