Question - How does inheritance work?
Answer -
HTML documents are structured hierarchically. There is an ancestor, the top level element, the HTML element, from which all other elements (children) are descended. As in any other family also children of the HTML family can inherit their parents, e.g. color or size.
By letting the children inherit their parents a default style can be created for top level elements and their children. (Note: not all properties can be inherited). The inheritance starts at the oldest ancestor and is passed on to its children and then their children and the children's children and so on.
Inherited style can be overridden by declaring specific style to child element. For example if the EM element is not to inherit its parent P then own style must be declared to it. For example:
BODY {font-size: 10pt}
All text will be displayed in a 10 point font
BODY {font-size: 10pt}
H1 {font-size: 14pt} or H1 {font-size: 180%}
All text except for the level 1 headings will be displayed in a 10 point font. H1 will be displayed in a 14 point font (or in a font that is 80% larger than the one set to BODY). If the element H1 contains other elements, e.g. EM then the EM element will also be displayed in a 14 point font (or 180%) it will inherit the property of the parent H1. If the EM element is to be displayed in some other font then own font properties must be declared to it, e.g.:
BODY {font-size: 10pt}
H1 {font-size: 14pt} or H1 {font-size: 180%}
EM {font-size: 15pt} or EM {font-size: 110%}
The EM element will be displayed in a 15 point font or will be 10% larger than H1. NOTE: EM is, in this example, inside H1 therefore will inherit H1's properties and not Body's.
The above declaration will display all EM elements in 15 point font or font that is 10% larger than font declared to the parent element. If this specific font is to apply to EM elements but only if they are inside H1 and not every occurrence of EM then EM must take a form of a contextual selector.
H1 EM {font-size: 15pt} or H1 EM {font-size: 110%}
In the example above EM is a contextual selector. It will be displayed in specified font only if it will