Although the picture at up-left seems to be slanting down to the left and the middle line at up-right seems to be curved, in fact all the brown and blue graphics on this page are squares positioned in straight, horizontal lines.

If you don't believe me, try running your mouse over them, carefully watching what happens. It all goes to show that some things are not what they seem...

Similarly, the vertical line that divides the blue and brown portions of this page is perfectly straight, but the variations in brightness may make it look otherwise.