Neon glow

The recipe is one colour and several shadows of it, stacked at growing blur radii and falling opacity: a tight bright halo that fakes the tube itself, then two or three wider washes that stand in for the light spilling into the air around it. Type uses text-shadow, a border uses box-shadow with no offset, and an irregular shape uses filter: drop-shadow() repeated, since that one follows the alpha channel rather than the box. Whatever the property, the core stays a light near-white or a very light tint of the hue and the halo carries the saturation, which is how real neon photographs: the tube blows out to white and the colour lives in the glow.

A dark background is not a stylistic preference here, it is a requirement. Glow is additive light, and light only reads as light when there is darkness for it to be brighter than. The same shadow stack on a white page turns into a smudge, which is the usual reason a neon treatment fails review. The effect is also uniquely tied to screens: it looks like what it is on an emissive display and disappears in print.

The connotations are consistent and worth using deliberately: nightlife and signage, arcades, synthwave, and the cyberpunk register generally. It overlaps with the Y2K aesthetic, though the two differ in what is doing the shining: Y2K’s brightness is specular, a highlight bouncing off chrome and plastic, while neon is emissive, coming from the element itself. Glow also does duty far outside the aesthetic, as the soft halo on a focus state, a live indicator, or a selected item in a dark theme.

Two limits. Glow adds no contrast, so the core colour has to pass on its own against the background and the halo counts for nothing in a measurement; a thin light halo around light-on-dark text can actually smear the letterforms and cost legibility at small sizes. And a stack of large blurred shadows is expensive to paint, especially animated, so the pulse that makes a sign feel alive belongs to one or two elements and belongs behind prefers-reduced-motion.