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CSS Basics: Selectors, Declarations, and Useful Elements

Learn the fundamentals of CSS such as rule structure, ID and class usage, table styling, and positioning elements using CSS properties. Understand display values and how to apply styles effectively.

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CSS Basics: Selectors, Declarations, and Useful Elements

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  1. SEEM4570Tutorial 3: CSS + CSS3.0 LI Xu xuli@se.cuhk.edu.hk 2019.10.04

  2. What is CSS ? • CSS stands for Cascading Style Sheets • CSS describes how HTML elements are to be displayed

  3. CSS Rule Structure CSS rule-set consists of a selector and a declaration block: • The selector points to the HTML element you want to style • The declaration block contains one or more declarations • Each declaration includes a CSS property name and a value • Each declaration separates with a semi-colon

  4. ID in CSS • Specify a style for a unique element by referring to the “id” in the HTML element. • The style is defined by “#” in CSS <head> <style> #para1{ color:red; } </style> </head> <body> <p id="para1">A style paragraph</p> <p id="para1">Another style paragraph</p> </body>

  5. Class in CSS • Specify a style for a unique of elements by referring to the “class” in the HTML element. • The style is defined by “.” in CSS <head> <style> .para1{ color:red; } </style> </head> <body> <p class="para1">A style paragraph</p> <p class="para1">Another style paragraph</p> </body>

  6. Some Useful Elements - Table • Table <table> • <th> head <tr>table row <td>table data • Table border • Table width and height • Table color • Alignment • Table Padding • Horizontal Dividers • Hoverable Table • Apply style to a specific table …

  7. Some Useful Elements - Table

  8. Some Useful Elements - Layer • We use <div> to represent it. • You need to understand the layout first:

  9. Some Useful Elements - Position • Position • Position properties allow you to position an element. It can also specify what should happen if an element’s content is too big or which element overlaps with one another. • There are four different position value: • Static(default) • Relative • Fixed • Absolute

  10. Some Useful Elements - Position • Position: relative • A relative positioned element is positioned relative to its normal position. • Example: • div.relative{ position: relative; left: 30px; border: 3px; }

  11. Some Useful Elements - Position • Position: fixed • A fixed positioned element is positioned relative to the browser window. • Example: • div.fixed{ position: fixed; bottom: 0; right: 0; width: 300px; border:3px; }

  12. Some Useful Elements - Position • Position: absolute • An absolute positioned element is positioned relative to the nearest positioned ancestor. If no such ancestor is found, it uses the document body, and move along with page scrolling. • Example: div.relative { position: relative; width: 400px; height: 200px; border: 3px; } div.absolute { position: absolute; bottom: 0; right: 0; width: 200px; height: 100px; border: 3px; } <div class="relative">This div element has position: relative; <div class="absolute">This div element has position: absolute;</div> </div>

  13. Some Useful Elements - Position • Position: overlapping • Elements can overlap other elements if needed. • The z-index property specifies the stack order of an element. • Example: img {    position: absolute;    left: 0px;    top: 0px;z-index: -1;}

  14. Some Useful Elements - Position

  15. Some Useful Elements - Display • Display property specifies how an element is displayed. • Commonly used values: div { display: inline; /* Default of all elements*/ display: inline-block; /* Characteristics of block, but sits on a line */ display: block; /* Display block-level element */ display: run-in; /* Not particularly well supported */ display: none; /* Hide */ }

  16. Some Useful Elements - Display • Inline • Don’t start on a new line and only take up as much width as necessary. It sits right inline with the natural flow of the text. • e.g. <span>、<em> 、<b>、<a> • Inline Block • Similar to inline element but is able to set a width and height • Block • Don’t sit inline but break past them. Take up as much horizontal space as they can. • e.g. <div>、<section>、<ul>、<h1> • Run-in • Make a header element to sit inline with the text below it. • Don’t work in Firefox

  17. Some Useful Elements - Display

  18. Some Useful Elements - Display • Table Values • Force non-table elements to behave like table-elements • Browser Support: • IE8 supports the "table-" values only if a !DOCTYPE is specified. div { display: table; /* like a <table> element*/ display: table-cell; /* like a <td> element*/ display: table-column; /* like a <col> element*/ display: table-column-group; /* like a <colgroup> element*/ display: table-header-group; /* like a <thead> element */ display: table-row-group; /* like a <tbody> element*/ display: table-footer-group; /* like a <tfoot> element*/ display: table-row; /*like a <tr> element */ display: table-caption; /* like a <caption> element*/ }

  19. Some Useful Elements - Display

  20. Some Useful Elements - Display Put together a multi-column layout

  21. What is CSS 3.0 ? • CSS 3.0 is the latest standard for CSS, and also completely backwards-compatible with earlier versions of CSS.

  22. Border-Radius Property • With CSS 3.0, you can give any element "rounded corners", by using the border-radius property. It is normally used like this:

  23. Border-Radius Property • Rules: • Four values: first value applies to top-left, second value applies to top-right, third value applies to bottom-right, and fourth value applies to bottom-left corner • Three values: first value applies to top-left, second value applies to top-right and bottom-left, and third value applies to bottom-right • Two values: first value applies to top-left and bottom-right corner, and the second value applies to top-right and bottom-left corner • One value: all four corners are rounded equally

  24. Backgrounds • CSS 3.0 allows you to add multiple background images for an element, through the background-image property. • The different background images are separated by commas, and the images are stacked on top of each other, where the first image is closest to the viewer.

  25. Backgrounds • Multiple background images can be specified using either the individual background properties (as above) or the background shorthand property. • The background-size property accepts multiple values for background size (using a comma-separated list), when working with multiple backgrounds.

  26. Colors • CSS supports color names, hexadecimal and RGB colors. In addition, CSS3 also introduces: RGBA colors, HSL colors, HSLA colors, opacity • RGBA Colors • an extension of RGB color values with an alpha channel - specifies the opacity for a color.

  27. Colors • HSL Colors • Hue, Saturation and Lightness. • Hue is a degree on the color wheel (0 - 360): • 0 (or 360) is red • 120 is green • 240 is blue • Saturation is a percentage value: 100% is the full color. • Lightness is also a percentage; 0% is dark (black) and 100% is white.

  28. Colors • HSLA Colors HSLA color values are an extension of HSL color values with an alpha channel - which specifies the opacity for a color. • Opacity Opacity property sets the opacity for the whole element (both background color and text will be opaque/transparent). And the opacity property value must be a number between 0.0 (fully transparent) and 1.0 (fully opaque).

  29. Gradients • CSS 3.0 gradients let you display smooth transitions between two or more specified colors. • CSS3 defines two types of gradients: • Linear Gradients (goes down/up/left/right/diagonally) • Radial Gradients (defined by their center) • Linear Gradients

  30. Gradients • Radial Gradients

  31. Shadow Effects • The CSS3 text-shadow property applies shadow to text. • In its simplest use, you only specify the horizontal shadow (2px) and the vertical shadow (2px): • Next, add a color to the shadow: • Then, add a blur effect to the shadow:

  32. Text • CSS 3.0 contains several new text features: • text-overflow • word-wrap • word-break • Text Overflow The CSS3 text-overflow property specifies how overflowed content that is not displayed should be signaled to the user.

  33. Text • Word Wrapping The CSS3 word-wrap property allows long words to be able to be broken and wrap onto the next line. • Word Breaking The CSS3 word-break property specifies line breaking rules.

  34. Animations • CSS 3.0 animations allows animation of most HTML elements without using JavaScript or Flash! • What are CSS 3.0 Animations? • An animation lets an element gradually change from one style to another. You can change as many CSS properties you want, as many times you want.

  35. Animations • To use CSS 3.0 animation, you must first specify some keyframes for the animation. Keyframes hold what styles the element will have at certain times. • The @keyframes Rule When you specify CSS styles inside the @keyframes rule, the animation will gradually change from the current style to the new style at certain times.

  36. Resources • http://www.w3schools.com/css/ • http://www.html.net/tutorials/css/ • http://www.barelyfitz.com/screencast/html-training/css/positioning/ • https://www.css3maker.com/

  37. Question Time

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