Building Blocks
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.
1- Block-level elements
start on a new line Examples include:
h1 p ul li
2- Inline elements
flow in between surrounding text Examples include:
img b i
Containing Elements
If one block-level element sits inside another block-level element then the outer box is known as the containing or parent element.
Controlling the Position of Elements
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.
To indicate where a box should be positioned, you may also need to use box offset properties to tell the browser how far from the top or bottom and left or right it should be placed.
Controlling the Position of Elements
Normal Flow
position:static
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
position:relative
Relative positioning moves an element in relation to where it would have been in normal flow
You then use the offset properties (top or bottom and left or right) to indicate how far to move the element from where it would have been in normal flow.
Absolute positioning
position:absolute
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
The box offset properties (top or bottom and left or right) specify where the element should appear in relation to its containing element.
Fixed positioning
position:Fixed
Fixed positioning is a type of absolute positioning that requires the position property to have a value of fixed.
It positions the element in relation to the browser window. Therefore, when a user scrolls down the page, it stays in the exact same place. It is a good idea to try this example in your browser to see the effect.
Overlapping Elements
z-index
When you use relative, fixed, or absolute positioning, boxes can overlap. If boxes do overlap, the elements that appear later in the HTML code sit on top of those that are earlier in the page. If you want to control which element sits on top, you can use the z-index property. Its value is a number, and the higher the number the closer that element is to the front. For example, an element with a z-index of 10 will appear over the top of one with a z-index of 5.
Floating Elements
The float property allows you to take an element in normal flow and place it as far to the left or right of the containing element as possible. Anything else that sits inside the containing element will flow around the element that is floated.
Clearing Floating The clear property allows you to say that no element (within the same containing element) should touch the left or righthand sides of a box.
If a containing element only contains floated elements, some browsers will treat it as if it is zero pixels tall.
Page Sizes
Because screen sizes and display resolutions vary so much, web designers often try to create pages of around 960-1000 pixels wide (since most users will be able to see designs this wide on their screens).
1- Fixed Width Layouts
Fixed width layout designs do not change size as the user increases or decreases the size of their browser window. Measurements tend to be given in pixels.
2- Liquid Layouts
Liquid layout designs stretch and contract as the user increases or decreases the size of their browser window. They tend to use percentages