ShaderMaterial shows error

I mix a picture texture,but it penetrated to the parent node div.
div with background red PG:

div without background PG:

If i do not set the gl_Fragcolor as same color.It shows normal.

If you set the alpha channel to something < 1 in gl_FragColor, you must set needAlphaBlending: true in the shader material constructor, else the color will be blended with the color of the CSS element instead of with what has already been rendered in the canvas: