1. Overview layer is positioned:
z-index: order of superimposed front and rear
2.position property:
3.fixed：
2.relative：
After moving:
static box1 not move up to occupy the position.
3.absolute：
After moving:
static move up to occupy the position of box1.
4.relative：
box1 relative static positioning.
5.absolute：
initial position:
absolute absolute movement relative to the rear:
After moving:
6. The general design approach:
Case:
the difference:
1. Overview layer is positioned:
z-index: order of superimposed front and rear
2.position property:
3.fixed：
2.relative：
After moving:
static box1 not move up to occupy the position.
3.absolute：
After moving:
static move up to occupy the position of box1.
4.relative：
box1 relative static positioning.
5.absolute：
initial position:
absolute absolute movement relative to the rear:
After moving:
6. The general design approach:
Case:
the difference: