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HTML

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CSS

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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

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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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HTML 

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

CSS 

              
                // #divtober 19: Nostalgia
// a.singlediv.com/divtober2021

black(alpha)
  rgba(0,0,0,alpha)

white(alpha)
  rgba(255,255,255,alpha)

$cracker-dot = radial-gradient(circle, saddlebrown 20%, alpha(saddlebrown,0) 40%),
               radial-gradient(circle, white(.35) 50%, white(0) 100%),
               radial-gradient(circle, alpha(peru,.2) 40%, alpha(peru,0) 100%)
$cracker-dot-size = 1em 1em, 1em 1em, 1em 1em
  
body
  min-height: 325tive
  background-color: rebeccapurple

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

  &:before,
  &:after
    display: block
    content: ''
    position: absolute
    
  @media (max-width: 400px)
    transform: scale(.8)

#nostalgia
  box-sizing: border-box
  font-size: 10px
  width: 35em
  height: 12em
  margin-left: -(@width/2)
  margin-top: -(@height/2)
  background-repeat: no-repeat
  background-image: linear-gradient(80deg, white(.2) 20%, white(0) 40%),
                    linear-gradient(to bottom, white(0), white(.2),
                                               white(.2), white(0)),
                    linear-gradient(to bottom, white(0), white(.2),
                                               white(.2), white(0)),
                    linear-gradient(to right, white(0), white(.2),
                                              white(.2), white(0)),
                    linear-gradient(to right, white(0), white(.2),
                                              white(.2), white(0)),
                    linear-gradient(to bottom, white(.25) 40%, white(.15) 50%),
                    linear-gradient(to right, alpha(rebeccapurple,0),
                                              darken(rebeccapurple,10),
                                              darken(rebeccapurple,10),
                                              alpha(rebeccapurple,0)),
                    linear-gradient(to right, alpha(rebeccapurple,0),
                                              darken(rebeccapurple,12),
                                              darken(rebeccapurple,12),
                                              alpha(rebeccapurple,0))
  background-size: 5% 20%,
                   .2em 40%,
                   .2em 40%,
                   20% .2em,
                   20% .2em,
                   100% 100%,
                   30% 50%,
                   40% 50%
  background-position: 1% 97%,
                       0 40%,
                       100% 0,
                       10% 0,
                       95% 100%,
                       0 0,
                       90% 0,
                       60% 100%
  box-shadow: 0 2em 0 -1em black(.2)

  &:before,
  &:after
    height: 10em
    top: 1em
    background-repeat: no-repeat
    border-radius: 2em

  &:before
    width: 9em
    left: 1em
    background-color: gold
    background-image: radial-gradient(circle, gold 50%, alpha(gold,0) 60%),
                      radial-gradient(circle, white(.5) 50%, white(0) 60%)
    background-size: 8em 8em,
                     5em 5em
    background-position: 70% 70%,
                         85% 85%
    box-shadow: inset 0 .3em .2em 0 white(.6),
                inset -.4em -.4em 0 black(.4),
                inset 0 0 0 .5em rebeccapurple,
                inset 1.2em 1.2em .4em black(.15)

  &:after
    width: 22.5em
    right: 1.5em
    background-color: rebeccapurple
    background-image: linear-gradient(90deg, crimson, lighten(crimson,10), crimson),
                      linear-gradient(darken(crimson,10), darken(crimson,10)),
                      $cracker-dot, $cracker-dot, $cracker-dot,
                      $cracker-dot, $cracker-dot, $cracker-dot,
                      $cracker-dot, $cracker-dot,
                      linear-gradient(to right, alpha(peru,.4),
                                                alpha(peru,0) 8%),
                      linear-gradient(to left, alpha(peru,.4),
                                                alpha(peru,0) 8%),
                      linear-gradient(to top, alpha(peru,.4),
                                                alpha(peru,0) 14%),
                      linear-gradient(-60deg, alpha(peru,.3), alpha(peru,0)),
                      linear-gradient(wheat, wheat),
                      repeating-linear-gradient(to bottom, darken(wheat,10),
                                                           darken(wheat,10) .4em,
                                                           transparent .4em,
                                                           transparent .8em),
                      repeating-linear-gradient(to right,  darken(wheat,10),
                                                           darken(wheat,10) .4em,
                                                           transparent .4em,
                                                           transparent .8em),
                      linear-gradient(darken(wheat,40), darken(wheat,40)),
                      repeating-linear-gradient(to bottom, darken(wheat,50),
                                                           darken(wheat,50) .4em,
                                                           transparent .4em,
                                                           transparent .8em),
                      repeating-linear-gradient(to right,  darken(wheat,50),
                                                           darken(wheat,50) .3em,
                                                           transparent .3em,
                                                           transparent .6em),
                      linear-gradient(20deg, black(.6) 0%,
                                             black(.4) 20%,
                                             black(.4) 50%,
                                             black(0) 60%),
                      linear-gradient(50deg, black(0) 70%, black(.3) 90%),
                      linear-gradient(white(.1), white(.1))
    background-size: 15em 3em,
                     15em 3.4em,
                     $cracker-dot-size, $cracker-dot-size, $cracker-dot-size,
                     $cracker-dot-size, $cracker-dot-size, $cracker-dot-size,
                     $cracker-dot-size, $cracker-dot-size,
                     18em 7em,
                     18em 7em,
                     18em 7em,
                     18em 7em,
                     18em 7em,
                     18.2em 7em,
                     18em 7.2em,
                     18em 7em,
                     18.4em 7em,
                     18em 7.2em,
                     100% 100%,
                     100% 100%,
                     100% 100%
    background-position: right 2.7em bottom 2.4em,
                         right 2.7em bottom 2em,
                         15% 25%, 14% 28%, 17% 25%,
                         15% 50%, 14% 53%, 17% 50%,
                         15% 75%, 14% 78%, 17% 75%,
                         29% 25%, 28% 28%, 31% 25%,
                         43% 25%, 41% 28%, 45% 25%,
                         57% 25%, 56% 28%, 59% 25%,
                         71% 25%, 70% 28%, 73% 25%,
                         85% 25%, 84% 28%, 87% 25%,
                         2.2em 50%,
                         2.2em 50%,
                         2.2em 50%,
                         2.2em 50%,
                         2.2em 50%,
                         2.1em 50%,
                         2.2em 50%,
                         1.8em 60%,
                         1.7em 60%,
                         1.8em 60%,
                         0 0,
                         0 0,
                         0 0
    box-shadow: inset .2em -.1em .1em .3em darken(rebeccapurple,5),
                inset -.1em .1em .1em .3em white(.6),
                inset .6em .1em .2em .3em white(.2),
                inset 0 -.5em .1em 0 white(.4),
                .5em 0 0 0 rebeccapurple
!

JS 

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

Console