::marker aligned to right

Sadly I think it’s a limitation of CSS and not currently possible. You could hide it with your CSS and add an image or something there using ::before or ::after but I don’t have any example code for you. It uses details HTML block so you should be able to search online.

Here is an example. When you use display property other than ‘list-item’, ::marker will not be shown. We’ll use flexbox to align the content

.lightweight-accordion .lightweight-accordion-title {
display: flex;
justify-content: space-between;
align-items: center;
}

Then it’s a matter of styling the custom marker that you want to show. Change ‘content’ value to whatever Unicode symbol you want to be a marker, or use background-image on ::after with width and height properties.

.lightweight-accordion .lightweight-accordion-title::after {
content: "\02C5";
color: #000;
font-size: 1.5rem;
margin-left: 2rem;
}