With a litle help from w3c shool 🙂 Hvorfor skriver vi noen ganger .center og noen ganger p.center (eller lignende)? Hva er det med det punktumet?
Slik jeg har forstått det er forklaringen denne:

skriver vi p.center{property: value}begrenser vi
class=center til bare å gjelde p elementer.

skriver vi .center{property: value} kan vi bruke
class=center for alle HTML elementer som div, p, etc.

Det samme gjelder for id (p#center, #center).
id kan bare brukes en gang i HTML koden mens
class kan brukes mange ganger.

Dette er hentet fra w3c schools:

The class Selector

With the class selector you can define different styles for the same type of HTML element.

Say that you would like to have two types of paragraphs in your document: one right-aligned paragraph, and one center-aligned paragraph. Here is how you can do it with styles:

p.right {text-align: right}
p.center {text-align: center}

You have to use the class attribute in your HTML document:

<p class="right">
This paragraph will be right-aligned.
</p>

<p class="center">
This paragraph will be center-aligned.
</p>

Note: To apply more than one class per given element, the syntax is:

<p class="center bold">
This is a paragraph.
</p>

The paragraph above will be styled by the class «center» AND the class «bold».

You can also omit the tag name in the selector to define a style that will be used by all HTML elements that have a certain class. In the example below, all HTML elements with class=»center» will be center-aligned:

.center {text-align: center}

In the code below both the h1 element and the p element have class=»center». This means that both elements will follow the rules in the «.center» selector:

<h1 class="center">
This heading will be center-aligned
</h1>

<p class="center">
This paragraph will also be center-aligned.
</p>