I use a theme called graphite that I slightly modified. Here is the full theme file:
Perso graphite:
# Graphite is a contemporary theme featuring a calming dark color scheme,
# native device fonts, and a cohesive design language.
# Designed to be visually appealing and easy on the eyes, it provides a
# consistent user experience across the entire home assistant interface,
# including the administration interface and code editors.
##############################################################################
# Tokens
# Color tokens
token-rgb-primary: 60, 175, 167 #229, 145, 9
token-color-primary: rgb(var(--token-rgb-primary))
token-color-primary-hexa: '#3CAFA7' #Le même en hexa
token-color-primary-light: rgb(143, 207, 205) #Ajout perso
token-color-primary-light-hexa: '#8FCFCD' #Le même en hexa
token-color-jaune-light: rgb(243, 243, 165) #Ajout perso
token-color-rouge-light: rgb(239, 129, 155) #Ajout perso
token-color-accent: var(--token-color-primary)
token-color-feedback-info: rgb(138, 208, 248)
token-color-feedback-warning: rgb(244,180,0)
token-color-feedback-error: rgb(229, 97, 128)
token-color-feedback-success: rgb(93, 193, 145)
token-color-icon-primary: rgba(228, 228, 231, 1)
token-color-icon-secondary: rgb(138 140 153)
token-color-icon-sidebar: rgba(147, 149, 159, 1)
token-color-icon-sidebar-selected: rgba(174, 176, 183, 1)
token-color-text-primary: rgba(228, 228, 231, 1)
token-color-text-secondary: rgb(138 140 153)
token-color-text-disabled: rgba(255, 255, 255, 0.5)
token-color-text-sidebar-selected: rgba(214, 215, 219, 1)
token-color-text-sidebar: var(--token-color-text-secondary)
token-color-text-label-badge: rgb(198, 203, 210)
token-color-background-base: rgba(22, 24, 29, 1)
token-color-background-secondary: rgba(28, 29, 33, 1)
token-color-background-sidebar: var(--token-color-background-base)
token-color-background-input-base: rgba(46, 48, 56, 1)
token-color-background-input-disabled: rgba(37, 37, 40, 0.5)
token-color-background-label-badge: rgba(54, 55, 67, 1)
token-color-background-card: rgba(37, 38, 45, 1)
token-color-background-card-light-hexa: '#505156' #Un peu plus clair en hexa
token-color-background-skrim: rgba(0, 0, 3, 0.9)
token-color-background-divider: var(--token-color-background-sidebar)
token-color-background-scrollbar-thumb: rgba(46, 48, 56, 1)
token-color-background-label-badge-red: var(--token-color-feedback-error)
token-color-background-label-badge-green: rgba(78, 183, 128, 1)
token-color-background-label-badge-blue: var(--token-color-feedback-info)
token-color-background-label-badge-yellow: var(--token-color-feedback-warning)
token-color-background-label-badge-grey: rgba(83, 90, 103, 1)
token-color-background-popup-scrim: rgba(4, 5, 7, 0.9)
token-color-border-card: rgba(0, 0, 0, 0)
# Opaciy tokens
token-opacity-ripple-hover: 0.14
# Font tokens
token-font-family-primary: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol"
# Size tokens
token-size-radius-small: 9px
token-size-radius-medium: 16px
token-size-radius-large: 18px
token-size-radius-card: var(--token-size-radius-large)
token-size-width-border-card: 0
token-size-height-slider: 4px
token-size-height-navbar: 56px
token-size-font-title: 28px
# Weight tokens
token-weight-font-title: 600
##############################################################################
# Definitions
# Shapes
mdc-shape-small: var(--token-size-radius-small)
mdc-shape-medium: var(--token-size-radius-medium)
mdc-shape-large: var(--token-size-radius-large)
# Sizes
header-height: var(--token-size-height-navbar)
paper-slider-height: var(--token-size-height-slider)
# Typography
primary-font-family: var(--token-font-family-primary)
paper-font-common-base_-_font-family: var(--token-font-family-primary)
paper-font-common-code_-_font-family: var(--token-font-family-primary)
paper-font-body1_-_font-family: var(--token-font-family-primary)
paper-font-subhead_-_font-family: var(--token-font-family-primary)
paper-font-headline_-_font-family: var(--token-font-family-primary)
paper-font-caption_-_font-family: var(--token-font-family-primary)
paper-font-title_-_font-family: var(--token-font-family-primary)
ha-card-header-font-family: var(--token-font-family-primary)
mdc-typography-font-family: var(--token-font-family-primary)
mdc-typography-button-font-family: var(--token-font-family-primary)
mdc-typography-body1-font-family: var(--token-font-family-primary)
mdc-typography-button-font-weight: var(--token-weight-font-title)
title-font-weight: var(--token-weight-font-title)
title-font-size: var(--token-size-font-title)
# Text
primary-text-color: var(--token-color-text-primary)
secondary-text-color: var(--token-color-text-secondary)
text-primary-color: var(--token-color-text-primary)
text-light-primary-color: var(--token-color-text-primary)
disabled-text-color: var(--token-color-text-disabled)
# Main interface colors
primary-color: var(--token-color-primary)
dark-primary-color: var(--primary-color)
light-primary-color: var(--primary-color)
accent-color: var(--token-color-accent)
divider-color: var(--token-color-background-divider)
scrollbar-thumb-color: var(--token-color-background-scrollbar-thumb)
# Feedback colors
error-color: rgb(234 114 135)
warning-color: rgb(255 219 117)
success-color: rgb(118 214 152)
info-color: rgb(39, 209, 246)
# Background
lovelace-background: var(--token-color-background-base)
background-color: var(--token-color-background-base)
primary-background-color: var(--token-color-background-base)
secondary-background-color: var(--token-color-background-secondary)
# Navbar
app-header-background-color: var(--primary-background-color)
app-header-text-color: var(--token-color-icon-primary)
app-header-edit-background-color: var(--token-color-background-card)
# Sidebar
sidebar-icon-color: var(--token-color-icon-sidebar)
sidebar-text-color: var(--sidebar-icon-color)
sidebar-background-color: var(--token-color-background-sidebar)
sidebar-selected-icon-color: var(--token-color-icon-sidebar-selected)
sidebar-selected-text-color: var(--token-color-text-sidebar-selected)
# Cards
border-radius: var(--token-size-radius-card)
card-background-color: var(--token-color-background-card)
ha-card-background: var(--token-color-background-card)
ha-card-border-radius: var(--token-size-radius-card)
ha-card-border-color: var(--token-color-border-card)
ha-card-border-width: var(--token-size-width-border-card)
ha-card-border-style: none
ha-card-border: none
ha-card-box-shadow: none
# States
state-icon-color: var(--token-color-icon-primary)
state-on-color: var(--token-color-feedback-success)
state-off-color: var(--token-color-feedback-error)
# Label-badge
label-badge-text-color: var(--token-color-text-primary)
label-badge-red: var(--token-color-background-label-badge-red)
label-badge-blue: var(--token-color-background-label-badge-blue)
label-badge-green: var(--token-color-background-label-badge-green)
label-badge-yellow: var(--token-color-background-label-badge-yellow)
label-badge-grey: var(--token-color-background-label-badge-grey)
# Chip
ha-chip-text-color: rgb(255 255 255)
# Dialog
mdc-dialog-scrim-color: var(--token-color-background-popup-scrim)
# Slider
paper-slider-knob-color: var(--token-color-primary)
paper-slider-knob-start-color: var(--paper-slider-knob-color)
paper-slider-pin-color: var(--paper-slider-knob-color)
paper-slider-active-color: var(--paper-slider-knob-color)
paper-slider-secondary-color: var(--light-primary-color)
# Switch
switch-checked-button-color: var(--primary-color)
switch-checked-track-color: var(--switch-checked-button-color)
switch-unchecked-button-color: rgba(255, 255, 255, 0.7)
switch-unchecked-track-color: rgba(125, 128, 132, 0.4)
# Toggles
paper-toggle-button-checked-button-color: var(--switch-checked-button-color)
paper-toggle-button-checked-bar-color: var(--switch-checked-track-color)
paper-toggle-button-unchecked-button-color: var(--switch-unchecked-button-color)
paper-toggle-button-unchecked-bar-color: var(--switch-unchecked-track-color)
mdc-checkbox-unchecked-color: var(--token-color-icon-secondary)
mdc-radio-unchecked-color: var(--mdc-checkbox-unchecked-color)
# List items
mdc-ripple-hover-opacity: var(--token-opacity-ripple-hover)
# Text Fields an Dropdown
input-background-color: var(--token-color-background-input-base)
input-background-token-color-disabled: rgba(var(--input-background-color), 0.5)
input-fill-color: var(--input-background-color)
input-ink-color: var(--token-color-text-primary)
input-label-ink-color: var(--token-color-text-primary)
input-disabled-fill-color: var(--input-background-token-color-disabled)
input-disabled-ink-color: var(--disabled-text-color)
input-disabled-label-ink-color: var(--disabled-text-color)
input-idle-line-color: var(--background-color)
input-dropdown-icon-color: var(--secondary-text-color)
input-hover-line-color: var(--primary-color)
mdc-select-idle-line-color: var(--color-background-base)
mdc-text-field-idle-line-color: var(--mdc-select-idle-line-color)
# Editor
code-editor-background-color: var(--token-color-background-base)
codemirror-meta: var(--token-color-text-primary)
codemirror-property: var(--accent-color)
codemirror-atom: var(--codemirror-property)
codemirror-string: rgb(119 196 229)
codemirror-keyword: rgb(140 169 255)
codemirror-number: rgb(255 91 29)
# RGB colors
rgb-primary-color: var(--token-rgb-primary)
rgb-accent-color: var(--token-rgb-primary)
rgb-white-color: 240, 243, 255
rgb-purple-color: 189, 157, 255
rgb-pink-color: 255, 98, 192
rgb-red-color: 255, 97, 116
rgb-deep-purple-color: 166, 77, 255
rgb-indigo-color: 84, 132, 255
rgb-blue-color: 33, 150, 243
rgb-light-blue-color: 3, 169, 244
rgb-cyan-color: 0, 188, 212
rgb-teal-color: 107, 255, 237
rgb-green-color: 141, 253, 166
rgb-light-green-color: 156, 255, 166
rgb-lime-color: 205, 220, 57
rgb-yellow-color: 255, 235, 59
rgb-amber-color: 255, 211, 99
rgb-orange-color: var(--rgb-primary-color)
rgb-deep-orange-color: 255, 87, 34
rgb-brown-color: 121, 85, 72
rgb-grey-color: 158, 158, 158
rgb-blue-grey-color: 96, 125, 139
rgb-black-color: 0, 0, 0
rgb-disabled-color: 61, 65, 85
rgb-state-inactive-color: 123, 126, 139
##############################################################################
# Extentions
# HACS
hacs-new-color: rgb(27 153 123)
hacs-error-color: rgb(182 46 95)
# Mini graph card
mcg-title-font-weight: 400
# Mushroom
mush-title-font-weight: var(--title-font-weight)
mush-title-font-size: var(--title-font-size)
mush-rgb-white: var(--rgb-white-color)
mush-rgb-purple: var(--rgb-purple-color)
mush-rgb-pink: var(--rgb-pink-color)
mush-rgb-red: var(--rgb-red-color)
mush-rgb-deep-purple: var(--rgb-deep-purple-color)
mush-rgb-indigo: var(--rgb-indigo-color)
mush-rgb-blue: var(--rgb-blue-color)
mush-rgb-light-blue: var(--rgb-light-blue-color)
mush-rgb-cyan: var(--rgb-cyan-color)
mush-rgb-teal: var(--rgb-teal-color)
mush-rgb-green: var(--rgb-green-color)
mush-rgb-light-green: var(--rgb-light-green-color)
mush-rgb-lime: var(--rgb-lime-color)
mush-rgb-yellow: var(--rgb-yellow-color)
mush-rgb-amber: var(--rgb-amber-color)
mush-rgb-orange: var(--rgb-orange-color)
mush-rgb-deep-orange: var(--rgb-deep-orange-color)
mush-rgb-brown: var(--rgb-brown-color)
mush-rgb-grey: var(--rgb-grey-color)
mush-rgb-blue-grey: var(--rgb-blue-grey-color)
mush-rgb-black: var(--rgb-black-color)
mush-rgb-disabled: var(--rgb-disabled-color)