Laying Out Elements with CSS

1. Laying out Elements with CSS

2. Objectives
Assess the CSS box model
Set element width and borders
Set margins and padding
Align elements with float
Control page flow with clear
HTML5 and CSS3 – Illustrated, 2nd Edition 2

3. Objectives (continued)
Implement fixed positioning
Implement relative positioning
Control stacking order
Implement absolute positioning
HTML5 and CSS3 – Illustrated, 2nd Edition 3

4. Assess the CSS Box Model
Box model: used by CSS to represent
characteristics of every web page
element
 Treats element as rectangular box
border: border surrounding element
margin: space from border to
neighboring/parent element
padding: space between border and
element content
HTML5 and CSS3 – Illustrated, 2nd Edition 4

5. Assess the CSS Box Model
(continued)
The CSS box model
HTML5 and CSS3 – Illustrated, 2nd Edition 5

6. Assess the CSS Box Model
(continued)
Box model properties
HTML5 and CSS3 – Illustrated, 2nd Edition 6

7. Assess the CSS Box Model
(continued)
CSS units of measure
 Relative units: ems, percent, rems
 Absolute units: pixels
Commonly used CSS units of
measure
HTML5 and CSS3 – Illustrated, 2nd Edition 7

8. Assess the CSS Box Model
(continued)
Size of padding, margin, and
border increase the amount of space
occupied by an element
 Dimensions of these properties not
included in specified width / height
• Specified width and height refer only to the
content of an element
• To calculate add the total space, add the
width value to the padding, margin, and
border values
HTML5 and CSS3 – Illustrated, 2nd Edition 8

9. Assess the CSS Box Model
(continued)
Calculating web page space occupied
by an element
HTML5 and CSS3 – Illustrated, 2nd Edition 9

10. Assess the CSS Box Model
(continued)
Collapse: When bottom margin of one
element is adjacent to top margin of
another, the margins combine to the
size of the larger of the two
 Affects element size planning
Separate property for each side of
padding and margin, e.g.
 padding-top: 2px;
 margin-right: 1em;
HTML5 and CSS3 – Illustrated, 2nd Edition 10

11. Set Element Width
and Borders
Margin, padding, and border are
shorthand properties
 Assign values to multiple CSS properties
 Assign values to all four sides of an
element
 Assign these values using a single
declaration
Can set width, style, or color of any or
all sides of an element
HTML5 and CSS3 – Illustrated, 2nd Edition 11

12. Set Element Width
and Borders (continued)
Specific properties for the box model
Reset rule: resets one or more
common properties to a common
baseline, e.g.
 border: 0
HTML5 and CSS3 – Illustrated, 2nd Edition 12

13. Set Element Width
and Borders (continued)
Code with width and border
declarations
HTML5 and CSS3 – Illustrated, 2nd Edition 13

14. Set Element Width
and Borders (continued)
width and border declarations
rendered in a browser and developer
tools opened to show box model
HTML5 and CSS3 – Illustrated, 2nd Edition 14

15. Set Margins and Padding
Use the shorthand property to assign
multiple values
 Separate each value with a space
 Meaning of different number of values
Assign auto to left and right margins
to center the element horizontally
HTML5 and CSS3 – Illustrated, 2nd Edition 15

16. Set Margins and Padding
(continued)
Example of padding using three
values and margin using two values
Example of margin set to auto
HTML5 and CSS3 – Illustrated, 2nd Edition 16

17. Align Elements with float
Page flow: the order of elements in the
HTML document
 User agents render HTML top to bottom
 Easy to create layouts with elements
stacked vertically
Use float, clear, and width
properties to create columns of text
and graphics parallel to each other
 Use width property to assign width to
each of the columns
HTML5 and CSS3 – Illustrated, 2nd Edition 17

18. Align Elements with float
(continued)
Example of float applied to element
Use float to create multicolumn
layoutsHTML5 and CSS3 – Illustrated, 2nd Edition 18

19. Align Elements with float
(continued)
Code with float and result in browser
HTML5 and CSS3 – Illustrated, 2nd Edition 19

20. Control Page Flow
with clear
float gives basic control over layout
clear gives more precise control
 Prevents floated elements from being
displayed to the left, right, or on the side
of another element
clear property values
HTML5 and CSS3 – Illustrated, 2nd Edition 20

21. Control Page Flow with clear
(continued)
Example of clear property
HTML5 and CSS3 – Illustrated, 2nd Edition 21

22. Control Page Flow with clear
(continued)
Code including clear property and
how it is rendered in a browser
HTML5 and CSS3 – Illustrated, 2nd Edition 22

23. Implement Fixed
Positioning
fixed positioning keeps an element
in the same location, even when the
page is scrolled
Use the position property with the
value of fixed
Then specify
 Horizontal position using left or right
 Vertical positing using top or bottom
HTML5 and CSS3 – Illustrated, 2nd Edition 23

24. Implement Fixed Positioning
(continued)
Commonly used position properties
Properties and values for fixed
positioning
HTML5 and CSS3 – Illustrated, 2nd Edition 24

25. Implement Fixed Positioning
(continued)
Example showing fixed positioning
HTML5 and CSS3 – Illustrated, 2nd Edition 25

26. Implement Fixed Positioning
(continued)
Code including fixed value and how
it is rendered in a browser
HTML5 and CSS3 – Illustrated, 2nd Edition 26

27. Implement Relative
Positioning
Relative positioning: adjusting default
position of an element
 Preserves space allotted to element in
default page flow
 Set position property to relative
 Style exact location using the properties
•left and right for horizontal positioning
•top and bottom for vertical positioning
HTML5 and CSS3 – Illustrated, 2nd Edition 27

28. Implement Relative
Positioning (continued)
CSS properties and values for relative
positioning
HTML5 and CSS3 – Illustrated, 2nd Edition 28

29. Implement Relative
Positioning (continued)
Implementing relative positioning and
page flow
HTML5 and CSS3 – Illustrated, 2nd Edition 29

30. Implement Relative
Positioning (continued)
Code using relative positioning and
how it is rendered in a browser
HTML5 and CSS3 – Illustrated, 2nd Edition 30

31. Control stacking order
Stacking elements: positioning
elements so that they can overlap
 Additional possibilities for layouts
 Applies only to positioned element
 Elements placed in new layer
 Requires careful planning
Stacking order controlled by values
assigned to z-index property
HTML5 and CSS3 – Illustrated, 2nd Edition 31

32. Control Stacking Order
(continued)
Stacking positioned elements
HTML5 and CSS3 – Illustrated, 2nd Edition 32

33. Control Stacking Order
(continued)
Code to stack and how it is
rendered in a browser
HTML5 and CSS3 – Illustrated, 2nd Edition 33

34. Implement Absolute
Positioning
Absolute positioning: takes element
out of page flow entirely
 Allows other elements to flow into space
element would have occupied
 Set position property to absolute
 Style exact location using left, right,
top, and bottom properties
 Location is calculated relative to closest
ancestor element that has position
applied to it
HTML5 and CSS3 – Illustrated, 2nd Edition 34

35. Implement Absolute
Positioning (continued)
Absolute positioning and page flow
Properties and values
HTML5 and CSS3 – Illustrated, 2nd Edition 35

36. Implement Absolute
Positioning (continued)
Code to absolutely position an
element and the result in a browser
HTML5 and CSS3 – Illustrated, 2nd Edition 36

37. Summary
Box model: used by CSS to represent
characteristics of elements
 Treats element as rectangular box
 Defines border, margin and padding
Margins of adjacent elements can
collapse into one margin
Specify border width, style,
and/or color of any or all sides
HTML5 and CSS3 – Illustrated, 2nd Edition 37

38. Summary (continued)
Use multiple values to assign margin
and padding values to different sides
Use float to change the default
page flow
Use clear to create a more precise
layout
Use float, clear and width to
create multicolumn layouts
HTML5 and CSS3 – Illustrated, 2nd Edition 38

39. Summary (continued)
Fixed positioning: keeps an element in
the same position, even when the
page is scrolled
Relative positioning: adjusting location
of element relative to its page flow
location using position property
 Space preserved
HTML5 and CSS3 – Illustrated, 2nd Edition 39

40. Summary (continued)
Use z-index to create a stacking
order for elements
 Stacked elements are placed in new
layers
Absolute positioning: takes elements
out of page flow entirely
 Other elements reflow into empty space
HTML5 and CSS3 – Illustrated, 2nd Edition 40