HTML Guide for stroke-width

Use a non-negative value for the CSS property stroke-width; negative lengths are invalid.

In SVG and CSS, the stroke-width property controls the thickness of the outline of shapes and text. It accepts non-negative numbers with optional units. A value of 0 is allowed (renders no visible stroke), but any negative value is invalid per the SVG and CSS specifications and will trigger validator errors.

You can specify stroke-width in user units (unitless, in the current SVG coordinate system) or with CSS length units like px. Common valid values: 0, 1, 2, 0.5, 3px. Avoid negative values and avoid quotes if you’re writing CSS; quotes are only appropriate inside HTML attributes when setting a style string.

If you were using a variable or calculation that could produce a negative number, clamp it to 0 or a minimum positive value.

HTML Examples

Example that reproduces the validator error

<p style="stroke-width: -1">some content</p>

Corrected example with a valid non-negative stroke width

<p style="stroke-width: 0">some content</p>