Actually, having a “dark” theme still isn’t possible yet. You can change quite a few variables for colours, but others are hard coded, for example the card and grid background colours. Making them use variables however is an easy fix and I’m sure I’ll be fixed in a short while.
So in the mean time, a proper “dark theme” isn’t available unfortunately. 
This can be done - a similar method is used in HADashboard for inserting CSS Strings in Jinja2. Maybe @andrey can base it off of that.
@PhysicalMagic what browser are you using?
I wonder if Stylish supports shadow dom. (Used in Chrome)
So when will it be available? How dark can you maximally go currently, which parts of the UI stay in a lighter colour palette? 
I have no idea when theming support will be more widely implemented.
You can make the background colour of the panel and pages other than the “State” page to whatever you like.
We’re currently working on a number of pull request changes to add more flexibility with colours for theming. Please see here: https://github.com/home-assistant/home-assistant-polymer/pull/361
Here’s two screenshots of where we currently stand – night and day themes:
Über like !
Do you reckon these will make 0.50.0?
Dark themes are now possible as of HA 0.51. 
Personally I like teal with dark colours.
https://community.home-assistant.io/t/dark-theme-or-night-mode-theme/446/37
I love the teal one - would you be willing to share it?
(Like the title of the thread implies…)
same here, nice work!
I have to make some changes and then I will post the code right here… 
In this topic you can find the codes for the darkcyan theme: "Dark" theme, or "night" mode/theme - #88
And here you can find the darkred theme: "Dark" theme, or "night" mode/theme - #53
Enjoy
Thanks; as soon as I saw the notification I grabbed it!
Theme loosely based off of the Solarized palette. Probably doesn’t meet criteria for Solarized but I really like the palette.
solarized:
primary-color: "#2aa198"
disabled-text-color: "#859900"
divider-color: "#586e75" #"rgba(255, 255, 255, 0.12)"
paper-card-background-color: "#002b36"
paper-grey-200: "#586e75"
paper-item-icon-color: "#b58900"
paper-listbox-background-color: "#002b36"
paper-listbox-color: "#b58900"
primary-background-color: "#073642"
primary-text-color: "#839496"
secondary-background-color: "#073642"
secondary-text-color: "#859900"
text-primary-color: "#839496"
label-badge-background-color: "var(--secondary-background-color)"
label-badge-text-color: "var(--text-primary-color)"
paper-card-header-color: "#cb4b16"
paper-grey-50: "#b58900"
paper-item-icon-active-color: "#dc322f"
paper-item-icon_-_color: "#FF00FF" # no clue
paper-slider-active-color: "#dc322f"
paper-slider-knob-color: "#dc322f"
paper-slider-knob-start-color: "#b58900"
paper-slider-pin-color: "#FF00FF" # no clue
paper-slider-secondary-color: "#dc322f"
paper-toggle-button-checked-ink-color: "#dc322f"
paper-toggle-button-checked-button-color: "#dc322f"
paper-toggle-button-checked-bar-color: "#cb4b16"
paper-toggle-button-unchecked-bar-color: "#b58900"
table-row-background-color: "#002b36"
table-row-alternative-background-color: "#073642"
google-red: "#dc322f"
google-green: "#859900"
google-blue: "#268bd2"
google-yellow: "#b58900"
accent-color: "#cb4b16"
paper-green: "#859900"
paper-blue: "#268bd2"
paper-orange: "#cb4b16"
Oh wow! Themes!
Thats great, gotta update 
One of the themes I recently made. Kind of a variant of the default theme. It’s still a WIP though, so there might be some issues with colours.
PmxDefault:
# Primary Color
primary-color: 'hsl(192, 96%, 48%)'
# Backgrounds
primary-background-color: 'hsl(0, 0%, 98%)'
secondary-background-color: 'hsl(0, 0%, 95%)'
paper-listbox-background-color: 'var(--primary-background-color)'
paper-card-background-color: 'var(--primary-background-color)'
paper-dialog-background-color: 'var(--primary-background-color)'
table-row-background-color: 'hsl(0, 0%, 96%)'
table-row-alternative-background-color: 'var(--primary-background-color)'
# Divider
divider-color: 'hsla(0, 0%, 0%, 0)'
dark-divider-opacity: '0'
light-divider-opacity: '0'
# Text colors
primary-text-color: 'hsl(0, 0%, 50%)'
text-primary-color: 'hsl(0, 0%, 60%)'
secondary-text-color: 'hsl(0, 0%, 60%)'
disabled-text-color: 'hsl(0, 0%, 70%)'
label-badge-border-color: 'hsl(0, 0%, 100%)'
sidebar-text_-_color: 'hsl(0, 0%, 90%)'
sidebar-text-color: 'hsl(0, 0%, 90%)'
# Text Adjustments
paper-font-headline_-_letter-spacing: '-0.5px'
paper-font-headline_-_font-weight: '500'
paper-font-body1_-_font-weight: '500'
# Nav Menu
paper-listbox-color: 'hsl(0, 0%, 85%)'
paper-grey-50: 'hsl(0, 0%, 85%)'
paper-grey-200: 'hsl(0, 0%, 95%)'
# Paper card
paper-card-header-color: 'hsla(0, 0%, 0%, 0.5)'
paper-item-icon-color: 'hsl(0, 0%, 80%)'
paper-item-icon-active-color: 'var(--paper-item-icon-color)'
paper-item-icon_-_color: 'var(--paper-item-icon-color)'
paper-item-selected_-_background-color: 'hsla(0, 0%, 0%, 0.2)'
paper-tabs-selection-bar-color: 'hsla(0, 0%, 0%, 0.2)'
ha-slider-background-color: 'var(--primary-background-color)'
paper-slider-bar-color: 'var(--primary-background-color)'
# Labels
label-badge-red: 'var(--primary-color)'
label-badge-background-color: 'var(--paper-card-background-color)'
label-badge-text-color: 'hsl(0, 0%, 60%)'
# Shadows
shadow-elevation-2dp_-_box-shadow: 'inset 0px 0px 0px 3px hsl(0, 0%, 88%)'
shadow-elevation-4dp_-_box-shadow: 'var(--shadow-elevation-2dp_-_box-shadow)'
shadow-elevation-6dp_-_box-shadow: 'var(--shadow-elevation-2dp_-_box-shadow)'
shadow-elevation-8dp_-_box-shadow: 'var(--shadow-elevation-2dp_-_box-shadow)'
shadow-elevation-10dp_-_box-shadow: 'var(--shadow-elevation-2dp_-_box-shadow)'
shadow-elevation-12dp_-_box-shadow: 'var(--shadow-elevation-2dp_-_box-shadow)'
shadow-elevation-14dp_-_box-shadow: 'var(--shadow-elevation-2dp_-_box-shadow)'
shadow-elevation-16dp_-_box-shadow: '0px 0px 0px 4px var(--primary-color)'
# Switches
paper-toggle-button-checked-button-color: 'hsl(192, 0%, 98%)'
paper-toggle-button-checked-bar-color: 'hsl(192, 0%, 50%)'
paper-toggle-button-unchecked-button-color: 'hsl(192, 0%, 98%)'
paper-toggle-button-unchecked-bar-color: 'hsl(192, 0%, 85%)'
# Sliders
paper-slider-knob-color: 'var(--primary-color)'
paper-slider-knob-start-color: 'hsl(0, 0%, 60%)'
paper-slider-pin-color: 'var(--primary-color)'
paper-slider-active-color: 'var(--primary-color)'
paper-slider-container-color: 'hsl(0, 0%, 90%)'
paper-slider-secondary-color: 'hsl(0, 0%, 90%)'
paper-slider-disabled-active-color: 'hsl(0, 0%, 90%)'
paper-slider-disabled-secondary-color: 'hsl(0, 0%, 90%)'
paper-dialog-color: 'hsl(0, 0%, 50%)'Anyone interested in a ‘way-too-early’ christmas theme?
I’ve got my homeassistant set-up to show this theme around the christmas period (nice theme + automation practice)
It still needs some touch-ups (e.g. slider & icon color on pop-ups for which I can 't seem to find the correct variables), but if people are interested I’ll post the code once I finish.
