varying vec2 vUv;
uniform vec3 uOuterColor;
uniform vec3 uInnerColor;

void main() {
    // Define the size of the white square as a proportion of the face
    float borderThickness = 0.2; // Adjust this value for border thickness
    if (vUv.x > borderThickness && vUv.x < 1.0 - borderThickness && vUv.y > borderThickness && vUv.y < 1.0 - borderThickness) {
        gl_FragColor = vec4(uInnerColor, 1.0); // Inner square
    } else {
        gl_FragColor = vec4(uOuterColor, 1.0); // Border
    }
}