compute --accent-foreground based on whether --foreground or --background have more contrast towards --accent-background

[michael]

CSS-only solutions:

https://svelte.dev/playground/hello-world?version=5.50.1#H4sIAAAAAAAAE4VT0YrbMBD8lUFQiIPtOFdaGiUNhFJoodeW5rHug2LLtogsGUvJXTjy74dOKMnFOfomZmdnZtfrJ6JYywklX9ZraCUP4G3XMCMMKt3zutc7VWLDDC-hFUpesZ202NTQPaqaxKQSkhtC_z4Re-ickgNIHHRXXZeaPZfWYU7nFl5oZbmyhlCyKMUehWTGfM6J0n3LZE6WP3_9uV_9WExKsV_m6hUn5M3J8uv972-r9fd14OVqYexBcve0tNfa4sk9gSTZsGLrp6PQW1k0oykyZNE8EM7jB0J2Iqjc5nYyRtEwVXPYxq2r1y14WqfI0jtYjSz9BKZKGM7R6AfYhqPQ0u1Nis5gPAlWYYREUtc1H-CFw6c3Cg3F3fuPQ3xTh9B71o8uHSJcIcUAaSK_hYGq6xd1Y6lbftuNshgFk8XohkmCLP0QYYzZbBbFmEbDjMIkJeu31GtMkVznCHZvxalq6heatOJx5MuAUH7yOABe9fy9I284NHNpXORplr2LrtrP1_Bmu88a-n27T37MFZD6Y3YX6GTPeZKXGegw59wzX5UvcryUj-4agfT01_5H_uJCbupfLPdksJj4v4jExPJHS6jtd_z4LyaWCfkgVEloxaThx2cGunMdTQQAAA

https://svelte.dev/playground/b7a3d94cb7c04dadb0447838995cde15?version=5.50.1#H4sIAAAAAAAAE31VbY6bMBC9ypOlSiEFkmzVqkuykaJtpVbaj2rzs_SHAQPWOibCTrqrKGfYC_QgPU8v0CtUhvAV2OaXGea9eW9mTA5E0g0jHrler5FJ8Qy22aZUcYU4y1mSZzsZIaCKRcgkIhbTndAIEmQ54oTYJOaCKeJ9PxD9vDVMJkDsine13bpqz4Q2McMzFA8zqZnUinhkEfE9QkGVuvKJzPINFT5Z3t0_3K5uFpOI75e-7ORUen2y_Hz77ctq_XVd5flyofSzYEtfAl6eZRoHcwQmY4RURjyimiHMRJYrjKiMoFPGc9wgTKmUTChQBbnbBCxXFsYTX_ra15Mx_vx6-fv7BdcplQkzKDgCeyp2TBVppojjBIkjPMzmOP2KSOhhOq-fUvNU5cdF_rSVH3fy4zq_rkDDx3JIHrJHEaajPc1HZWUL9TlsnVPLagrWM-7C4xY8bsHjCl63sV6XRkmrAdXbwpZ7McdA67gqGwedgbmJi9kQgemCO_s4771IPVy8-9CPB0nXUiOlMtNw9yJnJmNBEzWkiisnovmjZ7Zxsx1NbYRUhKPR1H0P55xUWBbGuLy8tGzMrL5ik8KTVHslyazPcCrXEleMpAKyvCekPU4Hrd0YlBKccXVldCp1GxSmWaYY4gQ89sqoIWy2gysY5cDq7lORpnAisnH_8AqiyCgQQRuB0dXyxGE4WW61RlMqceKkakXFPbWrU2GrLvlajzEetI23_0MWWQ2000-rAlq1kll5aAZwUm9296z5ta_O8OvahV_zHXM2_Kk2x2V5BeqCJ0f1rbfKMuclMMZsOn1jneGaKz6ECxpc29axVOuW33Ic0P5k9XjnpQuvr3RumAC3XpAhptbtP6dqtarkWkzKPwdiE82eNPF0vmPHHzbRlIufXEbEi6lQ7PgP-k_6jCQHAAA

https://svelte.dev/playground/b7a3d94cb7c04dadb0447838995cde15?version=5.50.1