<svg viewBox="0 0 600 120">
    <defs>
        <linearGradient id="rainbow" x1="0" x2="1">
            <stop offset="0" stop-color="#ff3b30"/>
            <stop offset="0.17" stop-color="#ff9500"/>
            <stop offset="0.34" stop-color="#ffcc00"/>
            <stop offset="0.51" stop-color="#4cd964"/>
            <stop offset="0.68" stop-color="#007aff"/>
            <stop offset="0.85" stop-color="#5856d6"/>
            <stop offset="1" stop-color="#ff2d55"/>
        </linearGradient>
    </defs>
    <rect width="100%" height="100%" fill="#ffffff"/>
    <text x="50%" y="55%" text-anchor="middle" font-size="44" fill="url(#rainbow)">Rainbow</text>
</svg>