multi-layer text-shadow
Text-shadow accepts more than one shadow in the same declaration: just separate each offset-x, offset-y, blur-radius and color group with a comma. Every extra layer adds typographic depth without an image or an extra filter, and the browser paints the first shadow in the list on top of the ones that follow, so the order you write the values in changes the final result.
Each layer adds 1px of offset over the previous one with no blur, and only the last layer carries a 6px blur to soften the letter base against the background.
The first two layers use a zero offset and a short blur to fake the neon tube white core, while the last two use a wider blur in the gas color to build the outer halo.
The light layer in the top-left corner fakes incoming light, and the larger, blurrier dark layer in the opposite corner anchors the text visually against the background.
Yes. The property takes a comma-separated list, painted front to back, the first shadow sits on top. That is how multi-layer outlines and glows are created.
There is no fixed limit in the specification, but every extra layer adds another blur and compositing pass to the element paint step; on a static heading, six to eight layers rarely matter, while on text animated by hover or scroll it is safer to keep the stack at three or four layers to avoid a stuttering repaint.
You likely typed a negative blur radius on one of the layers; the specification does not accept a negative blur-radius on any shadow in the list, and because that single value is invalid, the browser drops the whole declaration, not just the broken layer, which makes every shadow vanish at once.
Yes, as long as each unit is a valid CSS length, such as em, rem or vw; the only requirement is keeping the four values in the same order (horizontal offset, vertical offset, blur, color) and avoiding a mix of absolute and relative units inside one layer without checking the resulting effect at each screen size.
It still matters even with an identical offset, because order controls which layer sits visually on top; two overlapping shadows in different colors blend their appearance according to each one opacity, and whichever shadow is listed first always wins the implicit z-index dispute inside the text shadow stack.
color: #E6ECE8;
text-shadow: 3px 4px 8px #3DDC97,
6px 8px 10px #3DDC97,
9px 12px 12px #3DDC97;CSS is calculated locally; the text is not sent to the server.