`mix-blend-mode` relies on the parent container or its own background to participate in the mixing operation. If the element background is transparent (default value), the mixing will fail and the text will "disappear"; the key to the solution is to explicitly set the opaque `background-color`.

mix-blend-mode is a powerful CSS property that can be used to create dynamic text effects - such as automatically inverting titles on dark and light backgrounds (such as difference or exclusion modes). But a common misunderstanding is: only setting mix-blend-mode for text elements, but ignoring the need for its background to participate in the mixing .

CSS blending modes (such as difference, multiply, screen) work by mathematically combining the pixel values ​​of the current element with the background content in the stacking context below it . If the background of the element itself is transparent (this is the default value for block-level elements such as

and

), and its parent container has no background, there may be only a blank or (usually transparent) "below", resulting in a mixed result that is close to all black/all white/invisible - manifested as the text "disappearing".

✅ The correct approach is to explicitly declare a non-transparent background-color (even just a very light/dark color block) for the element with mix-blend-mode enabled , so that it has underlying pixels that can participate in the mixing. For example:

 .header {
  position: fixed;
  top: 10vh;
  width: 100%;
  z-index: 1000;
  mix-blend-mode: difference;
  background-color: rgba(255, 255, 255, 0.01); /* Very light white, invisible but involved in mixing*/
  /* Or use opaque colors (such as cadetblue) to ensure there is a basis for mixing */
}

⚠️ Notes:

• Do not set mix-blend-mode directly on the or root element, as it will affect all descendants and can easily cause accidental superposition;
• Make sure that .header and the background container (such as .fp-container-1 / .fp-container-2) are in the same stacking context (same level or reasonable z-index), otherwise blending may fail across levels;
• If you need more robust "background-independent visibility", you can combine text-shadow (such as text-shadow: 0 0 8px #000, 0 0 8px #000;) as a downgrade solution;
• mix-blend-mode is not supported in some older browsers (such as IE). It is recommended to add progressive enhancement logic in production environments.

Summary: mix-blend-mode is not a magic switch that "automatically adapts to the background", but a pixel-level calculation tool - its effect strictly depends on the comparison between the "current element background" and "its next layer content". Just remember: when setting blend, you must set background , and you can avoid 90% of the "text disappearing" problem.

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