I use IOS-Themes and I found the following, which may help with figuring out other themes: https://github.com/basnijholt/lovelace-ios-themes/issues/102
He added the following parameters to the theme:
DARK MODE:
mdc-theme-surface: "#2c2c2e"
material-background-color: "#2c2c2e"
ha-color-form-background: "#2c2c2e"
md-list-container-color: "none"
ha-color-on-neutral-normal: "#FFFFFF"
wa-color-neutral-fill-normal: "#FFFFFF14"
ha-color-fill-primary-quiet-resting: "rgba(255, 255, 255, 0.12)"
ha-color-fill-primary-quiet-hover: "rgba(255, 255, 255, 0.20)"
mdc-select-fill-color: "rgba(44, 44, 46, 0.95)"
mdc-select-ink-color: "#FFFFFF"
mdc-select-label-ink-color: "#d3d3d3"
mdc-select-dropdown-icon-color: "#d3d3d3"
mdc-select-idle-line-color: "#d3d3d3"
mdc-select-hover-line-color: "#FFFFFF"
mdc-select-focused-label-color: "rgba(255, 159, 9, 1)"
mdc-select-focused-dropdown-icon-color: "rgba(255, 159, 9, 1)"
mdc-select-focused-line-color: "rgba(255, 159, 9, 1)"
mdc-select-disabled-fill-color: "rgba(44, 44, 46, 0.5)"
mdc-select-disabled-ink-color: "#555"
mdc-select-disabled-dropdown-icon-color: "#555"
LIGHT MODE:
mdc-theme-surface: "#e5e5ea"
material-background-color: "#e5e5ea"
ha-color-form-background: "#e5e5ea"
md-list-container-color: "none"
ha-color-on-neutral-normal: "#464a47"
wa-color-neutral-fill-normal: "[#14](https://github.com/basnijholt/lovelace-ios-themes/issues/14)"
ha-color-fill-primary-quiet-resting: "rgba(0, 0, 0, 0.08)"
ha-color-fill-primary-quiet-hover: "rgba(0, 0, 0, 0.12)"
mdc-select-fill-color: "rgba(229, 229, 234, 0.95)"
mdc-select-ink-color: "#464a47"
mdc-select-label-ink-color: "#000000"
mdc-select-dropdown-icon-color: "#464a47"
mdc-select-idle-line-color: "#000000"
mdc-select-hover-line-color: "#464a47"
mdc-select-focused-label-color: "rgba(255, 159, 9, 1)"
mdc-select-focused-dropdown-icon-color: "rgba(255, 159, 9, 1)"
mdc-select-focused-line-color: "rgba(255, 159, 9, 1)"
mdc-select-disabled-fill-color: "rgba(229, 229, 234, 0.5)"
mdc-select-disabled-ink-color: "#555"
mdc-select-disabled-dropdown-icon-color: "#555"