De Stijl is a way people made art and buildings in the olden days, like when your great-grandparents were little. It started a long time ago in a place called the Netherlands, which is very far away.
De Stijl is all about using really simple shapes, like squares and rectangles, and making them look really cool by using only a few different colors. It's like if you had a lot of building blocks, and you only used some of them to make a picture.
De Stijl people thought that making really simple art and buildings would make the world a better place. They wanted everything to be really organized and easy to understand, like a game or a puzzle.
In De Stijl, everything has a place, and everything is in its place. It's kind of like when you clean up your toys and put them all away where they belong. That's how De Stijl buildings and art looks too, neat and tidy.
There are a lot of famous De Stijl artists, like Piet Mondrian, who made paintings with stripes of red, blue, and yellow, and used little squares to make the picture. Some buildings also followed De Stijl rules, like the Rietveld Schröder House, which used simple shapes and colors to make the building look really cool.
De Stijl was very important to art and design, and even today people still use its ideas to make things look simple and cool.