Gradient palette editor — #ac201d to #4000c9

/* https://grabient.com/_gJtgElgGJgIagKAgHqgNfgKjgIqgL-gLEgFa */

background: linear-gradient(90deg, #ac201d 0.000%, #ff9100 16.667%, #ffe000 33.333%, #cbe70b 50.000%, #54a449 66.667%, #163691 83.333%, #4000c9 100.000%);

<svg xmlns="http://www.w3.org/2000/svg" width="800" height="400" viewBox="0 0 800 400" preserveAspectRatio="none">
            <!-- https://grabient.com/_gJtgElgGJgIagKAgHqgNfgKjgIqgL-gLEgFa -->
            <defs>
              <linearGradient id="gradient" x1="0.000" y1="0.500" x2="1.000" y2="0.500">
        <stop offset="0.000" stop-color="#ac201d" /><stop offset="0.167" stop-color="#ff9100" /><stop offset="0.333" stop-color="#ffe000" /><stop offset="0.500" stop-color="#cbe70b" /><stop offset="0.667" stop-color="#54a449" /><stop offset="0.833" stop-color="#163691" /><stop offset="1.000" stop-color="#4000c9" />
              </linearGradient>
            </defs>
            <rect x="0" y="0" width="800" height="400" fill="url(#gradient)" />
          </svg>

["#ac201d", "#ff9100", "#ffe000", "#cbe70b", "#54a449", "#163691", "#4000c9"]

// https://grabient.com/_gJtgElgGJgIagKAgHqgNfgKjgIqgL-gLEgFa
// cosine gradient palette — https://iquilezles.org/articles/palettes/
const float STEPS = 7.0;
const float ANGLE = 90.0;

vec3 palette(float t) {
    vec3 a = vec3(0.621, 0.293, 0.393);
    vec3 b = vec3(0.538, 0.640, 0.490);
    vec3 c = vec3(0.863, 0.675, 0.554);
    vec3 d = vec3(0.766, 0.708, 0.346);
    return a + b * cos(6.283185 * (c * t + d));
}

// N stops sampled from the palette, blended like the CSS gradient
vec3 stops(float t) {
    float n = STEPS - 1.0;
    float x = clamp(t, 0.0, 1.0) * n;
    return mix(palette(floor(x) / n), palette(min(floor(x) + 1.0, n) / n), fract(x));
}

void mainImage(out vec4 fragColor, in vec2 fragCoord) {
    vec2 p = fragCoord - 0.5 * iResolution.xy;
    // CSS angle: 0 = up, clockwise; span = CSS gradient-line length
    vec2 dir = vec2(sin(radians(ANGLE)), cos(radians(ANGLE)));
    float len = abs(iResolution.x * dir.x) + abs(iResolution.y * dir.y);
    float t = dot(p, dir) / len + 0.5;
    fragColor = vec4(stops(t), 1.0);
}

[
  [0.621, 0.293, 0.393],
  [0.538, 0.640, 0.490],
  [0.863, 0.675, 0.554],
  [0.766, 0.708, 0.346]
]