There’s a slightly older version here covering Live Preview and Reading views:
Something more recent to cover Reading view:
ul:not(li > *) > li > .list-bullet::after { } /* level 1*/
ul:not(li > *) > li > ul > li > .list-bullet::after { } /* level 2 */
ul:not(li > *) > li > ul > li > ul > li> .list-bullet::after { } /* level 3 */
...
Combining it with Style Bullets in Lists by Level - #2 by rmdelatorre, you end up with the below. You could give that a try.
:root {
--bullet-new-color: purple;
}
/* level 1 - large bullet */
ul:not(li > *) > li > .list-bullet::after,
.HyperMD-list-line-1 .list-bullet:after {
height: 5px;
width: 5px;
border-radius: 50%;
background-color: var(--bullet-new-color);
}
/* level 2 - hyphen */
ul:not(li > *) > li > ul > li > .list-bullet::after,
.HyperMD-list-line-2 .list-bullet:after {
height: 1px;
width: 7px;
border-radius: 0%;
background-color: var(--bullet-new-color);
}
/* level 3 - hollow bullet */
ul:not(li > *) > li > ul > li > ul > li> .list-bullet::after,
.HyperMD-list-line-3 .list-bullet:after {
height: 4px;
width: 4px;
background-color: transparent;
border-color: var(--bullet-new-color);
border-style: solid;
border-radius: 50%;
border-width: 1px;
}
...