Here’s just something I worked on yesterday, so might as well share. The theme is as close to the Material dark theme guidelines as possible in Home Assistant currently. If there’s any issues, just let me know.
The theme has a customisable accent colour, simply change the value at the top of the theme and all colours should adjust accordingly.
dark:
# Accent Colour (Edit this to change the accent) #
accent: "#FF4081"
# Background
primary-background-color: "#121212"
# Text
primary-text-color: "#FFFFFFDE"
secondary-text-color: "#FFFFFF99"
disabled-text-color: "#FFFFFF61"
sidebar-selected-text-color: "var(--accent)"
# Card
card-background-color: "#1D1D1D"
paper-card-background-color: "#1D1D1D"
# Colours
primary-color: "#1D1D1D"
secondary-background-color: "#1D1D1D"
accent-color: "var(--accent)"
dark-primary-color: "var(--accent)"
light-primary-color: "var(--accent)"
# Controls
toggle-button-color: "var(--accent)"
paper-toggle-button-checked-button-color: "var(--accent)"
paper-toggle-button-checked-bar-color: "var(--accent)"
paper-toggle-button-checked-ink-color: "var(--accent)"
paper-toggle-button-unchecked-button-color: "#A5A5A5"
paper-toggle-button-unchecked-bar-color: "#787878"
paper-checkbox-checked-color: "var(--accent)"
paper-checkbox-checked-ink-color: "var(--accent)"
paper-radio-button-checked-color: "var(--accent)"
paper-input-container-focus-color: "var(--accent)"
paper-dropdown-menu-focus-color: "var(--accent)"
slider-color: "var(--accent)"
mdc-theme-primary: "var(--accent)"
# Icons
state-icon-color: "#A0A0A0"
state-icon-active-color: "var(--accent)"
sidebar-selected-icon-color: "var(--accent)"
sidebar-icon-color: "#A0A0A0"
# Badges
ha-label-badge-color: "var(--accent)"
label-badge-background-color: "#121212"
label-badge-text-color: "var(--secondary-text-color)"
# Tabs
paper-tab-ink: "var(--accent)"
# Divider
divider-color: "#2D2D2D"
# Lumo
lumo-base-color: "#2D2D2D"
lumo-tint-5pct: "none"
lumo-shade-5pct: "#272727"
paper-grey-200: "#272727"
lumo-primary-color-10pct: "#2D2D2D"
lumo-primary-color-50pct: "none"
lumo-box-shadow-m: "none"
lumo-primary-color: "var(--accent)"
lumo-header-text-color: "var(--primary-text-color)"
lumo-body-text-color: "var(--primary-text-color)"
lumo-tertiary-text-color: "var(--secondary-text-color)"
lumo-primary-contrast-color: "var(--primary-text-color)"