A clever CSS rule combining :invalid and :placeholder-shown to show validation state of non-empty input elements.
Topic: CSS – Page 14
Elements with overflow: hidden are scroll containers and can be scrolled programmatically.
The ex unit stands for x-height and refers to height of the lowercase "x" character of a font.
The defined pseudo class can be used to style not defined custom elements.
Today I learned that custom properties affect how invalid values influence the cascade