diff --git a/app/javascript/styles/full-dark.scss b/app/javascript/styles/full-dark.scss
new file mode 100644
index 0000000000..105964ba6f
--- /dev/null
+++ b/app/javascript/styles/full-dark.scss
@@ -0,0 +1,3 @@
+@import 'full-dark/variables';
+@import 'application';
+@import 'full-dark/diff';
diff --git a/app/javascript/styles/full-dark/diff.scss b/app/javascript/styles/full-dark/diff.scss
new file mode 100644
index 0000000000..1f97184eeb
--- /dev/null
+++ b/app/javascript/styles/full-dark/diff.scss
@@ -0,0 +1,9 @@
+input,
+textarea {
+  background: $ui-base-color !important;
+  color: $primary-text-color !important;
+}
+
+.emoji-mart-category-label {
+  color: $lighter-text-color !important;
+}
diff --git a/app/javascript/styles/full-dark/variables.scss b/app/javascript/styles/full-dark/variables.scss
new file mode 100644
index 0000000000..4e00d8a745
--- /dev/null
+++ b/app/javascript/styles/full-dark/variables.scss
@@ -0,0 +1,105 @@
+// Commonly used web colors
+$black: #000000; // Black
+$white: #ffffff; // White
+$red-600: #b7253d !default; // Deep Carmine
+$red-500: #df405a !default; // Cerise
+$blurple-600: #563acc; // Iris
+$blurple-500: #6364ff; // Brand purple
+$blurple-400: #7477fd; // Medium slate blue
+$blurple-300: #858afa; // Faded Blue
+$grey-600: #4e4c5a; // Trout
+$grey-100: #dadaf3; // Topaz
+
+$success-green: #79bd9a !default; // Padua
+$error-red: $red-500 !default; // Cerise
+$warning-red: #ff5050 !default; // Sunset Orange
+$gold-star: #ca8f04 !default; // Dark Goldenrod
+$kmyblue: #29a5f7 !default;
+
+$red-bookmark: $warning-red;
+
+// Values from the classic Mastodon UI
+$classic-base-color: #282c37; // Midnight Express
+$classic-primary-color: #9baec8; // Echo Blue
+$classic-secondary-color: #d9e1e8; // Pattens Blue
+$classic-highlight-color: #6364ff; // Brand purple
+
+// Values for kmyblue original functions
+$emoji-reaction-color: #42485a !default;
+$emoji-reaction-selected-color: #617ed5 !default;
+
+// Variables for defaults in UI
+$base-shadow-color: $black !default;
+$base-overlay-background: $black !default;
+$base-border-color: $white !default;
+$simple-background-color: $classic-base-color !default;
+$valid-value-color: $success-green !default;
+$error-value-color: $error-red !default;
+
+// Tell UI to use selected colors
+$ui-base-color: $classic-base-color !default; // Darkest
+$ui-base-lighter-color: #969fbc !default; // Lighter darkest
+$ui-primary-color: $classic-primary-color !default; // Lighter
+$ui-secondary-color: $classic-secondary-color !default; // Lightest
+$ui-highlight-color: $classic-highlight-color !default;
+$ui-button-color: $white !default;
+$ui-button-background-color: $blurple-500 !default;
+$ui-button-focus-background-color: $blurple-600 !default;
+$ui-button-focus-outline-color: $blurple-400 !default;
+$ui-button-focus-outline: solid 2px $ui-button-focus-outline-color !default;
+
+$ui-button-secondary-color: $grey-100 !default;
+$ui-button-secondary-border-color: $grey-100 !default;
+$ui-button-secondary-focus-background-color: $grey-600 !default;
+$ui-button-secondary-focus-color: $white !default;
+
+$ui-button-tertiary-color: $blurple-300 !default;
+$ui-button-tertiary-border-color: $blurple-300 !default;
+$ui-button-tertiary-focus-background-color: $blurple-600 !default;
+$ui-button-tertiary-focus-color: $white !default;
+
+$ui-button-destructive-background-color: $red-500 !default;
+$ui-button-destructive-focus-background-color: $red-600 !default;
+
+$ui-button-icon-focus-outline: $ui-button-focus-outline !default;
+$ui-button-icon-hover-background-color: rgba(140, 141, 255, 40%) !default;
+
+// Variables for texts
+$primary-text-color: $white !default;
+$darker-text-color: $ui-primary-color !default;
+$dark-text-color: $ui-base-lighter-color !default;
+$secondary-text-color: $ui-secondary-color !default;
+$highlight-text-color: lighten($ui-highlight-color, 8%) !default;
+$action-button-color: $ui-base-lighter-color !default;
+$action-button-focus-color: lighten($ui-base-lighter-color, 4%) !default;
+$passive-text-color: $gold-star !default;
+$active-passive-text-color: $success-green !default;
+
+// For texts on inverted backgrounds
+$inverted-text-color: $classic-secondary-color !default;
+$lighter-text-color: $ui-base-lighter-color !default;
+$light-text-color: $ui-primary-color !default;
+
+// Language codes that uses CJK fonts
+$cjk-langs: ja, ko, zh-CN, zh-HK, zh-TW;
+
+// Variables for components
+$media-modal-media-max-width: 100%;
+
+// put margins on top and bottom of image to avoid the screen covered by image.
+$media-modal-media-max-height: 80%;
+
+$no-gap-breakpoint: 1175px;
+
+$font-sans-serif: 'mastodon-font-sans-serif' !default;
+$font-display: 'mastodon-font-display' !default;
+$font-monospace: 'mastodon-font-monospace' !default;
+
+:root {
+  --dropdown-border-color: #{lighten($ui-base-color, 12%)};
+  --dropdown-background-color: #{lighten($ui-base-color, 4%)};
+  --dropdown-shadow: 0 20px 25px -5px #{rgba($base-shadow-color, 0.25)},
+    0 8px 10px -6px #{rgba($base-shadow-color, 0.25)};
+  --modal-background-color: #{darken($ui-base-color, 4%)};
+  --modal-border-color: #{lighten($ui-base-color, 4%)};
+}
diff --git a/config/locales/ja.yml b/config/locales/ja.yml
index d8c103c07f..7ab76e5b92 100644
--- a/config/locales/ja.yml
+++ b/config/locales/ja.yml
@@ -1817,6 +1817,7 @@ ja:
   themes:
     contrast: Mastodon (ハイコントラスト)
     default: Mastodon (ダーク)
+    full-dark: フルダーク
     mastodon-light: Mastodon (ライト)
   time:
     formats:
diff --git a/config/themes.yml b/config/themes.yml
index 9c21c9459f..7ba74bbd35 100644
--- a/config/themes.yml
+++ b/config/themes.yml
@@ -1,3 +1,4 @@
 default: styles/application.scss
 contrast: styles/contrast.scss
 mastodon-light: styles/mastodon-light.scss
+full-dark: styles/full-dark.scss