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HTML

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Adding Classes

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About the <head>

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Insecure Resource

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CSS

About CSS Preprocessors

CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.

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CSS Base

About CSS Base

It's a common practice to apply CSS to a page that styles elements such that they are consistent across all browsers. We offer two of the most popular choices: normalize.css and a reset. Or, choose Neither and nothing will be applied.

Vendor Prefixing

About Vendor Prefixing

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JavaScript

About JavaScript Preprocessors

JavaScript preprocessors can help make authoring JavaScript easier and more convenient.

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Babel includes JSX processing.

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Packages

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HTML 

              
                <div id="magic"></div>
!

CSS 

              
                // #divtober 21: Magic
// a.singlediv.com/divtober2021

white(alpha)
  rgba(255,255,255,alpha)
  
body
  min-height: 400px
  height: 100vh
  position: relative
  background-color: #bbb
  overflow: hidden
  font-size: 10px

div
  position: absolute
  left: 50%
  top: 50%

  &:before,
  &:after
    display: block
    content: ''
    position: absolute   

#magic
  width: 50%
  height: 240px
  left: -1em
  bottom: 0
  top: auto
  background-repeat: no-repeat
  background-image: radial-gradient(circle, white 50%, white(0) 51%),
                    radial-gradient(circle, white 50%, white(0) 51%),
                    radial-gradient(circle, white 50%, white(0) 51%),
                    radial-gradient(circle, white 50%, white(0) 51%),
                    radial-gradient(circle, white 50%, white(0) 51%)
  background-size: .5em .5em,
                   .6em .6em,
                   1em 1em,
                   .6em .6em,
                   .7em .7em
  background-position: right  6em  top 6em,
                       right 12em  top 8em,
                       right  2em  top 8em,
                       right  4em  top 10em,
                       right 2.4em top 13em
  border-top-right-radius: 25em 10em
  box-shadow: 1em  -2em 0 crimson,
              1em  -4em 0 orange,
              1em  -6em 0 gold,
              1em  -8em 0 seagreen,
              1em -10em 0 cornflowerblue,
              1em -12em 0 rebeccapurple

  &:before
    width: 100%
    height: 100%
    left: auto
    right: calc((100% + 2em) * -1)
    bottom: 0
    background-repeat: no-repeat
    background-image: radial-gradient(circle, white 50%, white(0) 51%),
                      radial-gradient(circle, white 50%, white(0) 51%),
                      radial-gradient(circle, white 50%, white(0) 51%),
                      radial-gradient(circle, white 50%, white(0) 51%),
                      radial-gradient(circle, white 50%, white(0) 51%),
                      radial-gradient(circle, white 50%, white(0) 51%)
    background-size: 1em 1em,
                     .5em .5em,
                     .6em .6em,
                     .6em .6em,
                     .7em .7em,
                     .5em .5em
    background-position:  6em  6em,
                         10em  9em,
                          2em  8em,
                          8em  12em,
                         2.2em 15em,
                         15em 3em
    border-top-left-radius: 25em 10em
    box-shadow: -1em  -2em 0 crimson,
                -1em  -4em 0 orange,
                -1em  -6em 0 gold,
                -1em  -8em 0 seagreen,
                -1em -10em 0 cornflowerblue,
                -1em -12em 0 rebeccapurple

  &:after
    width: 24em
    height: 24em
    right: -13em
    bottom: -7em
    border-radius: 50%
    background-repeat: no-repeat
    background-image: linear-gradient(to right, #ddd 40%, white 40%),
                      linear-gradient(to right, #222 40%, #444 40%),
                      linear-gradient(white, white),
                      linear-gradient(white, white),
                      linear-gradient(white, white),
                      linear-gradient(white, white),
                      radial-gradient(circle, white 50%, white(0) 51%),
                      radial-gradient(circle, white 50%, white(0) 51%)
    background-size: 3em 4em,
                     3em 15em,
                     1.5em .3em,
                     .3em 1.5em,
                     1.5em .3em,
                     .3em 1.5em,
                     .6em .6em,
                     1em 1em
    background-position: 50% calc(50% - 5.5em),
                         50% 50%,
                         5em 9em,
                         5.6em 8.4em,
                         right 6em top 4em,
                         right 6.6em top 3.4em,
                         49% 7%,
                         51% 12%
    box-shadow:  2.3em -13.6em 0 -11.7em white,
                 0.3em -15.6em 0 -11.5em white,
                 5.0em -15.5em 0 -11.8em white,
                 3.0em -16.5em 0 -11.8em white,
                 8.0em -19.5em 0 -11.8em white,
                 3.3em -20.0em 0 -11.6em white,
                 6.2em -22.5em 0 -11.8em white,
                 2.2em -22.2em 0 -11.8em white,
                12.2em -22.2em 0 -11.8em white,
                20.0em -25.7em 0 -11.8em white,
                 0.5em -25.5em 0 -11.7em white,
                 -3.0em -14.6em 0 -11.7em white,
                 -1.0em -19.6em 0 -11.7em white,
                 -4.4em -23.6em 0 -11.7em white,
                 -5.4em -20.2em 0 -11.8em white,
                -10.4em -20.2em 0 -11.6em white,
                 -8.4em -27.1em 0 -11.8em white,
                -20.4em -27.7em 0 -11.8em white
!

JS 

              
                // @lynnandtonic
// a.singlediv.com
!
999px

Console