CSS treats each HTML element as if it is in its own box. This box will either be a block-level box or an inline box.
If one block-level element sits inside another block-level element then the outer box is known as the containing or parent element.
CSS has the following positioning schemes that allow you to control the layout of a page: normal flow, relative positioning, and absolute positioning. You specify the positioning scheme using the position property in CSS. You can also float elements using the float property.
Every block-level element appears on a new line, causing each item to appear lower down the page than the previous one. Even if you specify the width of the boxes and there is space for two elements to sit side-byside, they will not appear next to each other. This is the default behavior (unless you tell the browser to do something else).
This moves an element from the position it would be in normal flow, shifting it to the top, right, bottom, or left of where it would have been placed. This does not affect the position of surrounding elements; they stay in the position they would be in in normal flow.
This positions the element in relation to its containing element. It is taken out of normal flow, meaning that it does not affect the position of any surrounding elements (as they simply ignore the space it would have taken up). Absolutely positioned elements move as users scroll up and down the page.
In normal flow, each block-level element sits on top of the next one. Since this is the default way in which browsers treat HTML elements, you do not need a CSS property to indicate that elements should appear in normal flow.
Relative positioning moves an element in relation to where it would have been in normal flow.
When the position property is given a value of absolute, the box is taken out of normal flow and no longer affects the position of other elements on the page.
Different visitors to your site will have different sized screens that show different amounts of information, so your design needs to be able to work on a range of different sized screens.
