The official CSSoc website.

• px
  • Pixels (px) are relative to the viewing device. For low-dpi devices, 1px is one device pixel (dot) of the display. For printers and high resolution screens 1px implies multiple device pixels.
• %
• vw, vh
  • Always include px as well (to support ancient browsers) like so:
    • height: 75px; height: 8vh;
• em
  • Only for input forms.

• Maximum height of sponsor logo: 120px.
• Social media icons: 60px × 60px.
• Header icon: 50px × 50px.

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