/* https://grabient.com/_gJCgE0gH0gVMgDdgZIgBogBmgBggDDgLMgK9?style=linearGradient&steps=5&angle=135 */

background: linear-gradient(135deg, #ff4303 0.000%, #d24c3f 25.000%, #9a557d 50.000%, #625dbb 75.000%, #2b66f7 100.000%);

<svg xmlns="http://www.w3.org/2000/svg" width="800" height="400" viewBox="0 0 800 400" preserveAspectRatio="none">
            <!-- https://grabient.com/_gJCgE0gH0gVMgDdgZIgBogBmgBggDDgLMgK9?style=linearGradient&steps=5&angle=135 -->
            <defs>
              <linearGradient id="gradient" x1="0.146" y1="0.146" x2="0.854" y2="0.854">
        <stop offset="0.000" stop-color="#ff4303" /><stop offset="0.250" stop-color="#d24c3f" /><stop offset="0.500" stop-color="#9a557d" /><stop offset="0.750" stop-color="#625dbb" /><stop offset="1.000" stop-color="#2b66f7" />
              </linearGradient>
            </defs>
            <rect x="0" y="0" width="800" height="400" fill="url(#gradient)" />
          </svg>

["#ff4303", "#d24c3f", "#9a557d", "#625dbb", "#2b66f7"]

// https://grabient.com/_gJCgE0gH0gVMgDdgZIgBogBmgBggDDgLMgK9?style=linearGradient&steps=5&angle=135
// cosine gradient palette — https://iquilezles.org/articles/palettes/
const float STEPS = 5.0;
const float ANGLE = 135.0;

vec3 palette(float t) {
    vec3 a = vec3(0.578, 0.308, 0.500);
    vec3 b = vec3(1.356, 0.221, 1.608);
    vec3 c = vec3(0.104, 0.102, 0.096);
    vec3 d = vec3(0.195, 0.716, 0.701);
    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);
}

[
  [0.578, 0.308, 0.500],
  [1.356, 0.221, 1.608],
  [0.104, 0.102, 0.096],
  [0.195, 0.716, 0.701]
]

Gradient palette editor — #ff4303 to #2b66f7