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HTML 

              
                html
body.onepage
    section#section-1.section.vertical
      div
        h1 A first section
        |         
        svg.svg(xmlns='http://www.w3.org/2000/svg', width='300', height='300', viewbox='0 0 32 32')
          path(d='M12 20l4-2 14-14-2-2-14 14-2 4zm-2.959 7.097c-.989-2.085-2.052-3.149-4.137-4.137l3.097-8.525 4-2.435 12-12h-6l-12 12-6 20 20-6 12-12v-6l-12 12-2.435 4z', fill='#ffc7c7')
        |         
        p Orders from the menu &amp; by the left and right keys.
    |     
    |     
    section#section-2.section.vertical
      div
        h2 A second section
        |         
        svg.svg(xmlns='http://www.w3.org/2000/svg', width='300', height='300', viewbox='0 0 32 32')
          path(d='M22.423 0c-5.274 8.718-9.447 4.431-15.55 10.701-5.386 5.533-3.518 12.197 1.016 14.492 4.476-2.287 9.055-7.401 12.452-14.804 0 0 3.052 9.348-6.297 18.355 4.54 5.317 12.245 1.618 14.398-6.841 2.341-9.196-3.762-18.559-6.019-21.903zm-19.391 30.195c.004.091.107 1.805 2.355 1.805 1.636 0 9.932-4.521 14.196-16.256-6.451 11.413-15.816 14.245-16.551 14.451z', fill='#a163cc')
        |         
        p Intermediate section...
    |     
    |     
    section#section-3.section.vertical
      div
        h2 A third section
        |         
        svg.svg(xmlns='http://www.w3.org/2000/svg', width='300', height='300', viewbox='0 0 32 32')
          path(d='M14.533 19.422l-10.578-10.578c-5.273 6.086-5.273 15.07 0 21.156l10.578-10.578zm1.467-1.422v-18c-4.906.305-9.328 2.18-12.897 5.102l12.897 12.898zm2.002-13.984v14.812l-10.383 10.383c2.328 1.711 5.133 2.789 8.235 2.789 7.818 0 14.146-6.328 14.146-14.133 0-7.078-5.227-12.812-11.998-13.851z', fill='#cbffc7')
        |         
        p Congratulations, you managed without incident until the last level!
    |     
    |     
    nav.main-nav
      a(href='#section-1') Section 1
      |       
      a(href='#section-2') Section 2
      |       
      a(href='#section-3') Section 3
!

CSS 

              
                html
  scroll-behavior: smooth

.onepage
  & .section
    box-sizing border-box
    min-height 100vh
    margin 0
    padding 1em 2em
    &:nth-child(3n+1)
      color #ffc7c7
      background-color #ba5959
      & *
        color #ffc7c7
        fill #ffc7c7
    &:nth-child(3n+2)
      color #a163cc
      background-color #4b2e5f
      & *
        color #a163cc
        fill #a163cc
    &:nth-child(3n+3)
      color #cbffc7
      background-color #61ba59
      & *
        color #cbffc7
        fill #cbffc7
  & .main-nav
    position fixed
    z-index 4000
    display table
    table-layout fixed
    bottom 0
    text-align center
    background rgba(0, 0, 0, .2)
    @media (max-width: 40em)
        width 100%
    @media (min-width 40em)
        top 0
        right 0
    & a
      display table-cell
      padding 1rem
      color #fefefe
      text-decoration none
      &.active
        background-color rgba(0, 0, 0, 0.3)

// for demo:

@import url(https://fonts.googleapis.com/css?family=Open+Sans)

html
body
  box-sizing border-box
  height:100%
  margin 0
  padding 0
  color #fefefe
  font-family 'Open Sans', Arial

.vertical
  display table
  width 100%
  height 100% // @bugfix @affected Firefox
  & > *
    display table-cell
    vertical-align middle
    text-align center

p
  font-size 1.2em

h1
.h1
  margin-top 1.6em
  margin-bottom 0.8em
  font-size 3.2em

h2
.h2
  margin-top 1.4em
  margin-bottom 0.7em
  font-size 2.8em

@media (max-width 40em)
  
  h1
  .h1
    font-size 9.6vmin

  h2
  .h2
    font-size 7.6vmin

.svg
  display block
  margin 5vh auto 0
  width 100%
  height 100%
  max-width 30wh
  max-height 30vh
!

JS 

              
                // No JS
!
999px

Console