あまりスマートではありませんが、こんな形にすることは可能です。
:root {
--lcv-name-color: rgba(255,255,255,1);
--lcv-text-color: rgba(255,255,255,1);
--lcv-background-color: rgba(255,255,255,0);
--lcv-name-shadow: var(--lcv-name-shadow-3);
--lcv-name-shadow-color: rgba(255,255,255,1);
--lcv-comment-shadow: var(--lcv-comment-shadow-3);
--lcv-comment-shadow-color: rgba(255,255,255,1);
}
[data-service="niconama"] {
--lcv-name-shadow: 3px 0px 0.5px rgba(37,37,37,1), 2.83745px 0.974098px 0.5px rgba(37,37,37,1), 2.36742px 1.84264px 0.5px rgba(37,37,37,1), 1.64084px 2.5115px 0.5px rgba(37,37,37,1), 0.736456px 2.9082px 0.5px rgba(37,37,37,1), -0.247738px 2.98975px 0.5px rgba(37,37,37,1), -1.20509px 2.74732px 0.5px rgba(37,37,37,1), -2.03184px 2.20717px 0.5px rgba(37,37,37,1), -2.63842px 1.42784px 0.5px rgba(37,37,37,1), -2.95908px 0.493784px 0.5px rgba(37,37,37,1), -2.95908px -0.493784px 0.5px rgba(37,37,37,1), -2.63842px -1.42784px 0.5px rgba(37,37,37,1), -2.03184px -2.20717px 0.5px rgba(37,37,37,1), -1.20509px -2.74732px 0.5px rgba(37,37,37,1), -0.247738px -2.98975px 0.5px rgba(37,37,37,1), 0.736456px -2.9082px 0.5px rgba(37,37,37,1), 1.64084px -2.5115px 0.5px rgba(37,37,37,1), 2.36742px -1.84264px 0.5px rgba(37,37,37,1), 2.83745px -0.974098px 0.5px rgba(37,37,37,1);
--lcv-comment-shadow: 3px 0px 0.5px rgba(37,37,37,1), 2.83745px 0.974098px 0.5px rgba(37,37,37,1), 2.36742px 1.84264px 0.5px rgba(37,37,37,1), 1.64084px 2.5115px 0.5px rgba(37,37,37,1), 0.736456px 2.9082px 0.5px rgba(37,37,37,1), -0.247738px 2.98975px 0.5px rgba(37,37,37,1), -1.20509px 2.74732px 0.5px rgba(37,37,37,1), -2.03184px 2.20717px 0.5px rgba(37,37,37,1), -2.63842px 1.42784px 0.5px rgba(37,37,37,1), -2.95908px 0.493784px 0.5px rgba(37,37,37,1), -2.95908px -0.493784px 0.5px rgba(37,37,37,1), -2.63842px -1.42784px 0.5px rgba(37,37,37,1), -2.03184px -2.20717px 0.5px rgba(37,37,37,1), -1.20509px -2.74732px 0.5px rgba(37,37,37,1), -0.247738px -2.98975px 0.5px rgba(37,37,37,1), 0.736456px -2.9082px 0.5px rgba(37,37,37,1), 1.64084px -2.5115px 0.5px rgba(37,37,37,1), 2.36742px -1.84264px 0.5px rgba(37,37,37,1), 2.83745px -0.974098px 0.5px rgba(37,37,37,1);
}
[data-service="twitch"] {
--lcv-name-shadow: 3px 0px 0.5px rgba(100,65,165,1), 2.83745px 0.974098px 0.5px rgba(100,65,165,1), 2.36742px 1.84264px 0.5px rgba(100,65,165,1), 1.64084px 2.5115px 0.5px rgba(100,65,165,1), 0.736456px 2.9082px 0.5px rgba(100,65,165,1), -0.247738px 2.98975px 0.5px rgba(100,65,165,1), -1.20509px 2.74732px 0.5px rgba(100,65,165,1), -2.03184px 2.20717px 0.5px rgba(100,65,165,1), -2.63842px 1.42784px 0.5px rgba(100,65,165,1), -2.95908px 0.493784px 0.5px rgba(100,65,165,1), -2.95908px -0.493784px 0.5px rgba(100,65,165,1), -2.63842px -1.42784px 0.5px rgba(100,65,165,1), -2.03184px -2.20717px 0.5px rgba(100,65,165,1), -1.20509px -2.74732px 0.5px rgba(100,65,165,1), -0.247738px -2.98975px 0.5px rgba(100,65,165,1), 0.736456px -2.9082px 0.5px rgba(100,65,165,1), 1.64084px -2.5115px 0.5px rgba(100,65,165,1), 2.36742px -1.84264px 0.5px rgba(100,65,165,1), 2.83745px -0.974098px 0.5px rgba(100,65,165,1);
--lcv-comment-shadow: 3px 0px 0.5px rgba(100,65,165,1), 2.83745px 0.974098px 0.5px rgba(100,65,165,1), 2.36742px 1.84264px 0.5px rgba(100,65,165,1), 1.64084px 2.5115px 0.5px rgba(100,65,165,1), 0.736456px 2.9082px 0.5px rgba(100,65,165,1), -0.247738px 2.98975px 0.5px rgba(100,65,165,1), -1.20509px 2.74732px 0.5px rgba(100,65,165,1), -2.03184px 2.20717px 0.5px rgba(100,65,165,1), -2.63842px 1.42784px 0.5px rgba(100,65,165,1), -2.95908px 0.493784px 0.5px rgba(100,65,165,1), -2.95908px -0.493784px 0.5px rgba(100,65,165,1), -2.63842px -1.42784px 0.5px rgba(100,65,165,1), -2.03184px -2.20717px 0.5px rgba(100,65,165,1), -1.20509px -2.74732px 0.5px rgba(100,65,165,1), -0.247738px -2.98975px 0.5px rgba(100,65,165,1), 0.736456px -2.9082px 0.5px rgba(100,65,165,1), 1.64084px -2.5115px 0.5px rgba(100,65,165,1), 2.36742px -1.84264px 0.5px rgba(100,65,165,1), 2.83745px -0.974098px 0.5px rgba(100,65,165,1);
}
[data-service="youtube"] {
--lcv-name-shadow: 3px 0px 0.5px rgba(255,0,0,1), 2.83745px 0.974098px 0.5px rgba(255,0,0,1), 2.36742px 1.84264px 0.5px rgba(255,0,0,1), 1.64084px 2.5115px 0.5px rgba(255,0,0,1), 0.736456px 2.9082px 0.5px rgba(255,0,0,1), -0.247738px 2.98975px 0.5px rgba(255,0,0,1), -1.20509px 2.74732px 0.5px rgba(255,0,0,1), -2.03184px 2.20717px 0.5px rgba(255,0,0,1), -2.63842px 1.42784px 0.5px rgba(255,0,0,1), -2.95908px 0.493784px 0.5px rgba(255,0,0,1), -2.95908px -0.493784px 0.5px rgba(255,0,0,1), -2.63842px -1.42784px 0.5px rgba(255,0,0,1), -2.03184px -2.20717px 0.5px rgba(255,0,0,1), -1.20509px -2.74732px 0.5px rgba(255,0,0,1), -0.247738px -2.98975px 0.5px rgba(255,0,0,1), 0.736456px -2.9082px 0.5px rgba(255,0,0,1), 1.64084px -2.5115px 0.5px rgba(255,0,0,1), 2.36742px -1.84264px 0.5px rgba(255,0,0,1), 2.83745px -0.974098px 0.5px rgba(255,0,0,1);
--lcv-comment-shadow: 3px 0px 0.5px rgba(255,0,0,1), 2.83745px 0.974098px 0.5px rgba(255,0,0,1), 2.36742px 1.84264px 0.5px rgba(255,0,0,1), 1.64084px 2.5115px 0.5px rgba(255,0,0,1), 0.736456px 2.9082px 0.5px rgba(255,0,0,1), -0.247738px 2.98975px 0.5px rgba(255,0,0,1), -1.20509px 2.74732px 0.5px rgba(255,0,0,1), -2.03184px 2.20717px 0.5px rgba(255,0,0,1), -2.63842px 1.42784px 0.5px rgba(255,0,0,1), -2.95908px 0.493784px 0.5px rgba(255,0,0,1), -2.95908px -0.493784px 0.5px rgba(255,0,0,1), -2.63842px -1.42784px 0.5px rgba(255,0,0,1), -2.03184px -2.20717px 0.5px rgba(255,0,0,1), -1.20509px -2.74732px 0.5px rgba(255,0,0,1), -0.247738px -2.98975px 0.5px rgba(255,0,0,1), 0.736456px -2.9082px 0.5px rgba(255,0,0,1), 1.64084px -2.5115px 0.5px rgba(255,0,0,1), 2.36742px -1.84264px 0.5px rgba(255,0,0,1), 2.83745px -0.974098px 0.5px rgba(255,0,0,1);
}
この例ではrootで指定されているshadow-3の太さに合わせているため、別の太さにする場合は調整が必須です。