Qin Shihuang unified the use of "Xiao Zhuan", but at the same time "Li Shu" also rose. Li Shu has two sources: 1. Slaves write in prison. In order to save time, the seal script is also simplified, because it is more troublesome to write seal script and the requirements for radian are stricter. Li Shu actually turned the small seal script into a horizontal seal script, so it was called Li Shu.
Although Qin Shihuang unified the writing, many people didn't like Xiao Zhuan because the writing of Xiao Zhuan was too troublesome. In order to consolidate his reform achievements, Qin Shihuang had to conform to public opinion, so he stipulated that "official documents must use Xiao Zhuan, but official scripts can be used at ordinary times". That's not official script. Official script belongs to Xiao Zhuan and was later called official script.
Calligraphy became an art in the late Eastern Han Dynasty, and it is still an official font.
Zhong You, a great calligrapher in Wei and Jin Dynasties, changed his previous calligraphy and created regular script which was easier to write.
Qin Gui in the Southern Song Dynasty created the font "Song Ti", which is widely used in printing now. If he hadn't killed Yue Fei, this Song Zi would be called Qin Zi.
In the final analysis, the current fonts are all based on the previous fonts, and the current simplified characters are found from ancient cursive scripts and running scripts. If you look carefully at the ancient cursive script, many words are almost the same as the simplified words now, especially next to the words "Yan" and "door".