This is a Fully Define Sketch because sketch is not moving by pulling the corner. Part file is attached.
It is colour change of the sketch and indication in right corner bottom of screen tell us it is a "Fully Define Sketch".
Here it is easy to find out even though color did not change, because sketch is a simple one. How to find out if sketch is a complex one in a 3D sketch.
Hi Maha:
Please delete the 45-degree dimension add Along Z relation for this line to fully define the sketch.
Regards
Shaodun Lin