CSS from the future

210a2116d2266c84d155f1d8a14f31ef?s=47 FEVR
February 23, 2017
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CSS from the future

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FEVR

February 23, 2017
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Transcript

  1. One step in the future: CSS Variables version ✌

  2. None

  3. Giacomo Zinetti Giko

  4. Action plan • • • • • • •

  5. Theory

  6. Define --your-property: value;

  7. How to define a property :root { --button-color: blue; --align:

    left; } header { --header-height: 300px; }

  8. Use var(--your-property, default-value)

  9. How to use a variable button { background-color: var(--button-color); }

    a { color: var(--link-color, black); }

  10. Quiz time: Inherited or not?

  11. Quiz time: Inherited or not?

  12. VS Preprocessors

  13. <body> <a>Link 1</a> <footer> <a>Link 2</a> </footer> </body> Inheritance :root

    { --link: red } footer { --link: blue } a { color: var(--link) } <body> <a>Link 1</a> <footer> <a>Link 2</a> </footer> </body> $link: red footer { $link: blue } a { color: $link }

  14. <body> <a>Link 1</a> <footer> <a>Link 2</a> </footer> </body> Inheritance compiled

    :root { --link: red } footer { --link: blue } a { color: var(--link) } <body> <a>Link 1</a> <footer> <a>Link 2</a> </footer> </body> $link: red footer { $link: blue } a { color: $link red }

  15. <body> <a>Link 1</a> <footer> <a>Link 2</a> </footer> </body> Inheritance :root

    { --link: red } footer { --link: blue } a { color: var(--link) } <body> <a>Link 1</a> <footer> <a>Link 2</a> </footer> </body> $link: red footer { $link: blue } a { color: $link } Preprocessors: Nope

  16. :root { --gutter: 10px; } @media (min-width: 768px) { :root

    { --gutter: 15px; } } article { padding: var(--gutter); } Media queries $gutter: 10px; @media (min-width: 768px) { $gutter: 15px; } article { padding: $gutter; }

  17. :root { --gutter: 10px; } @media (min-width: 768px) { :root

    { --gutter: 15px; } } article { padding: var(--gutter); } Media queries compiled $gutter: 10px; @media (min-width: 768px) { $gutter: 15px; } article { padding: $gutter 10px; }

  18. :root { --gutter: 10px; } @media (min-width: 768px) { :root

    { --gutter: 15px; } } article { padding: var(--gutter); } Media queries $gutter: 10px; @media (min-width: 768px) { $gutter: 15px; } article { padding: $gutter; } Preprocessors: Nope

  19. :root { --gutter: 10px; } @media (min-width: 768px) { :root

    { --gutter: 15px; } } article { padding: var(--gutter); } Preprocessors solution $gutter: 10px; $gutter-large: 15px; @media (min-width: 768px) { article { padding: $gutter-large; } } article { padding: $gutter; }

  20. But… :root { --gutter: 10px; } @media (min-width: 768px) {

    :root { --gutter: 15px; } } article.class { padding: var(--gutter); } $gutter: 10px; $gutter-large: 15px; @media (min-width: 768px) { article { padding: $gutter-large; } } article.class { padding: $gutter; }

  21. But… they can be friends

  22. Example

  23. <body> <a>Link 1</a> <footer> <a>Link 2</a> <section> <a>Link 3</a> </section>

    </footer> </body> Base rule a { background: var(--link, red) }

  24. <body> <a>Link 1</a> <footer> <a>Link 2</a> <section> <a>Link 3</a> </section>

    </footer> </body> Override variables, not properties section { --link: green } a { background: var(--link, red) }

  25. <body> <a>Link 1</a> <footer> <a>Link 2</a> <section> <a>Link 3</a> </section>

    </footer> </body> Make Cascade Love, not Specificity War section { --link: green } footer { --link: blue } a { background: var(--link, red) }

  26. Old school... section { --link: green } footer { --link:

    blue } a { background: var(--link, red) } footer section a { background: green } footer a { background: blue } a { background: red } <body> <a>Link 1</a> <footer> <a>Link 2</a> <section> <a>Link 3</a> </section> </footer> </body>

  27. Old school... section { --link: green } footer { --link:

    blue } a { background: var(--link, red) } -------------- footer section a { background: green } footer a { background: blue } a { background: red } <body> <a>Link 1</a> <footer> <a>Link 2</a> <section> <a>Link 3</a> </section> </footer> </body> The end of specificity war!

  28. Javascript

  29. Read getComputedStyle(element).getPropertyValue('--color'); element.style.setProperty('--color', 'red'); Write

  30. Support

  31. Browsers 49+ 31+ 15? 36+ 9.1+ Jan 2017: 68.34%

  32. Fallback property @supports (--foo: green) { body { color: var(--my-color);

    } } Feature query color: red; color: var(--my-color, red);

  33. Good news

  34. <body> <a>Link 1</a> <footer> <a>Link 2</a> <section> <a>Link 3</a> </section>

    </footer> </body> We already use CSS variables body { font-size: 18px } footer { font-size: 16px } section { font-size: 14px } a { border-width: 0.2em; padding-right: 2em; }

  35. <body> <a>Link 1</a> <footer> <a>Link 2</a> <section> <a>Link 3</a> </section>

    </footer> </body> The superhero: currentColor body { color: red } footer { color: blue } section { color: green } a { border-color: currentColor; }

  36. Use case: Theming

  37. .theme(@bg: gray, @col: red, @var: blue) { .box { background:

    @bg } .button { color: @col } .box .button { color: @var } } .theme(); .dark { .theme(black, orange, lightgreen); } Theming with LESS

  38. .box { background: gray } .button { color: red }

    .box .button { color: blue } .dark .box { background: black } .dark .button { color: orange } .dark .box .button { color: lightgreen } Theming with CSS

  39. .box { --col: var(--alt, blue); background: var(--bg, lightgray); } .button

    { color: var(--col, red); } .dark { --bg: black; --col: orange; --alt: lightgreen; } Theming with CSS Variables

  40. Questions?

  41. Grazie! @giacomozinetti