vaadin-checkbox.css

/* Dividers */

:host([theme~="dividers"]) {
    position: relative;
}

:host([theme~="dividers"]:not(:last-of-type))::after {
    border-bottom: 1px solid var(--lumo-contrast-10pct);
    content: "";
    inset: auto 0 0 0;
    pointer-events: none;
    position: absolute;
}

/* Align: Right */

:host([theme~="align-right"]) .vaadin-checkbox-container {
    grid-template-columns: 1fr auto;
}

:host([theme~="align-right"]) [part='checkbox'],
:host([theme~="align-right"]) ::slotted(input) {
    grid-column: 2;
}

:host([theme~="align-right"][has-label]) ::slotted(label) {
    padding-inline-start: 0;
}

/* Switch */

:host([theme~="switch"]) [part='checkbox'] {
    border-radius: 9999px;
    width: var(--lumo-size-m);
}

:host([theme~="switch"]) [part='checkbox']::after {
    content: "";
    height: calc(var(--lumo-size-m) / 3);
    background-color: var(--lumo-secondary-text-color);
    border-radius: 9999px;
    inset: 0;
    /* (size-m/2 - size-m/3) / 2 = size-m/12 */
    margin: calc(var(--lumo-size-m) / 12);
    opacity: 1;
    transition: transform 0.2s;
    width: calc(var(--lumo-size-m) / 3);
}

:host([theme~="switch"][checked]) [part='checkbox']::after {
    background-color: var(--lumo-primary-contrast-color);
    /* size-m - size-m/3 - 2*size-m/12 = size-m/2 */
    transform: translateX(calc(var(--lumo-size-m) / 2));
}