Use CSS variables for themes (#528)

* Update formatting

* Merge default tag color with category-less tags

* Use CSS variables for colors

* Add dark theme colors

* Move color variables into display.css

* Remove old stylesheets

* Update headings

* Bump minimum Firefox version to support CSS var()

* Revert popular kanji text color

3 files changed, 166 insertions, 224 deletions

diff --git a/ext/mixed/css/display-dark.css b/ext/mixed/css/display-dark.css
deleted file mode 100644
index acfa2782..00000000
--- a/ext/mixed/css/display-dark.css
+++ /dev/null
@@ -1,103 +0,0 @@
-/*
- * Copyright (C) 2019-2020  Yomichan Authors
- *
- * This program is free software: you can redistribute it and/or modify
- * it under the entrys of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program.  If not, see <https://www.gnu.org/licenses/>.
- */
-
-
-body { background-color: #1e1e1e; color: #d4d4d4; }
-
-h2 { border-bottom-color: #2f2f2f; }
-
-.navigation-header {
-    background-color: #1e1e1e;
-    border-bottom-color: #2f2f2f;
-}
-
-.entry+.entry { border-top-color: #2f2f2f; }
-
-.kanji-glyph-data>tbody>tr>* { border-top-color: #3f3f3f; }
-
-.tag { color: #e1e1e1; }
-.tag[data-category=default]      { background-color: #69696e; }
-.tag[data-category=name]         { background-color: #489148; }
-.tag[data-category=expression]   { background-color: #b07f39; }
-.tag[data-category=popular]      { background-color: #025caa; }
-.tag[data-category=frequent]     { background-color: #4490a7; }
-.tag[data-category=archaism]     { background-color: #b04340; }
-.tag[data-category=dictionary]   { background-color: #9057ad; }
-.tag[data-category=frequency]    { background-color: #489148; }
-.tag[data-category=partOfSpeech] { background-color: #565656; }
-.tag[data-category=search]       { background-color: #69696e; }
-.tag[data-category=pitch-accent-dictionary] { background-color: #6640be; }
-
-.term-reasons { color: #888888; }
-
-.term-expression>.term-expression-text .kanji-link {
-    border-bottom-color: #888888;
-    color: #cccccc;
-}
-
-.term-expression[data-frequency=popular]>.term-expression-text,
-.term-expression[data-frequency=popular]>.term-expression-text .kanji-link {
-    color: #0275d8;
-}
-
-.term-expression[data-frequency=rare]>.term-expression-text,
-.term-expression[data-frequency=rare]>.term-expression-text .kanji-link {
-    color: #666666;
-}
-
-.term-definition-list,
-.term-pitch-accent-group-list,
-.term-pitch-accent-disambiguation-list,
-.kanji-glossary-list {
-    color: #888888;
-}
-
-.term-glossary,
-.term-pitch-accent,
-.kanji-glossary {
-    color: #d4d4d4;
-}
-
-.icon-checkbox:checked + label {
-    /* invert colors */
-    background-color: #d4d4d4;
-    color: #1e1e1e;
-}
-
-.term-pitch-accent-container { border-bottom-color: #2f2f2f; }
-
-.term-pitch-accent-character:before { border-color: #ffffff; }
-
-.term-pitch-accent-graph-line,
-.term-pitch-accent-graph-line-tail,
-#term-pitch-accent-graph-dot,
-#term-pitch-accent-graph-dot-downstep,
-#term-pitch-accent-graph-triangle {
-    stroke: #ffffff;
-}
-
-#term-pitch-accent-graph-dot,
-#term-pitch-accent-graph-dot-downstep>circle:last-of-type {
-    fill: #ffffff;
-}
-
-.term-glossary-image-container {
-    background-color: #2f2f2f;
-}
-.term-glossary-image-container-overlay {
-    color: #888888;
-}
diff --git a/ext/mixed/css/display-default.css b/ext/mixed/css/display-default.css
deleted file mode 100644
index 70f81eb6..00000000
--- a/ext/mixed/css/display-default.css
+++ /dev/null
@@ -1,103 +0,0 @@
-/*
- * Copyright (C) 2019-2020  Yomichan Authors
- *
- * This program is free software: you can redistribute it and/or modify
- * it under the entrys of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program.  If not, see <https://www.gnu.org/licenses/>.
- */
-
-
-body { background-color: #ffffff; color: #333333; }
-
-h2 { border-bottom-color: #eeeeee; }
-
-.navigation-header {
-    background-color: #ffffff;
-    border-bottom-color: #eeeeee;
-}
-
-.entry+.entry { border-top-color: #eeeeee; }
-
-.kanji-glyph-data>tbody>tr>* { border-top-color: #dddddd; }
-
-.tag { color: #ffffff; }
-.tag[data-category=default]      { background-color: #8a8a91; }
-.tag[data-category=name]         { background-color: #5cb85c; }
-.tag[data-category=expression]   { background-color: #f0ad4e; }
-.tag[data-category=popular]      { background-color: #0275d8; }
-.tag[data-category=frequent]     { background-color: #5bc0de; }
-.tag[data-category=archaism]     { background-color: #d9534f; }
-.tag[data-category=dictionary]   { background-color: #aa66cc; }
-.tag[data-category=frequency]    { background-color: #5cb85c; }
-.tag[data-category=partOfSpeech] { background-color: #565656; }
-.tag[data-category=search]       { background-color: #8a8a91; }
-.tag[data-category=pitch-accent-dictionary] { background-color: #6640be; }
-
-.term-reasons { color: #777777; }
-
-.term-expression>.term-expression-text .kanji-link {
-    border-bottom-color: #777777;
-    color: #333333;
-}
-
-.term-expression[data-frequency=popular]>.term-expression-text,
-.term-expression[data-frequency=popular]>.term-expression-text .kanji-link {
-    color: #0275d8;
-}
-
-.term-expression[data-frequency=rare]>.term-expression-text,
-.term-expression[data-frequency=rare]>.term-expression-text .kanji-link {
-    color: #999999;
-}
-
-.term-definition-list,
-.term-pitch-accent-group-list,
-.term-pitch-accent-disambiguation-list,
-.kanji-glossary-list {
-    color: #777777;
-}
-
-.term-glossary,
-.term-pitch-accent,
-.kanji-glossary {
-    color: #000000;
-}
-
-.icon-checkbox:checked + label {
-    /* invert colors */
-    background-color: #333333;
-    color: #ffffff;
-}
-
-.term-pitch-accent-container { border-bottom-color: #eeeeee; }
-
-.term-pitch-accent-character:before { border-color: #000000; }
-
-.term-pitch-accent-graph-line,
-.term-pitch-accent-graph-line-tail,
-#term-pitch-accent-graph-dot,
-#term-pitch-accent-graph-dot-downstep,
-#term-pitch-accent-graph-triangle {
-    stroke: #000000;
-}
-
-#term-pitch-accent-graph-dot,
-#term-pitch-accent-graph-dot-downstep>circle:last-of-type {
-    fill: #000000;
-}
-
-.term-glossary-image-container {
-    background-color: #eeeeee;
-}
-.term-glossary-image-container-overlay {
-    color: #777777;
-}
diff --git a/ext/mixed/css/display.css b/ext/mixed/css/display.css
index 4f43af6f..8b567173 100644
--- a/ext/mixed/css/display.css
+++ b/ext/mixed/css/display.css
@@ -15,6 +15,72 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+/*
+ * Variables
+ */
+
+:root {
+    --background-color: #ffffff;
+    --glossary-image-background-color: #eeeeee;
+
+    --dark-text-color: #000000;
+    --default-text-color: #333333;
+    --light-text-color: #777777;
+    --very-light-text-color: #999999;
+
+    --light-border-color: #eeeeee;
+    --medium-border-color: #dddddd;
+    --dark-border-color: #777777;
+
+    --popuplar-kanji-text-color: #0275d8;
+
+    --pitch-accent-annotation-color: #000000;
+
+    --tag-text-color: #ffffff;
+    --tag-default-background-color: #8a8a91;
+    --tag-name-background-color: #5cb85c;
+    --tag-expression-background-color: #f0ad4e;
+    --tag-popular-background-color: #0275d8;
+    --tag-frequent-background-color: #5bc0de;
+    --tag-archaism-background-color: #d9534f;
+    --tag-dictionary-background-color: #aa66cc;
+    --tag-frequency-background-color: #5cb85c;
+    --tag-part-of-speech-background-color: #565656;
+    --tag-search-background-color: #8a8a91;
+    --tag-pitch-accent-dictionary-background-color: #6640be;
+}
+
+:root[data-yomichan-theme=dark] {
+    --background-color: #1e1e1e;
+    --glossary-image-background-color: #2f2f2f;
+
+    --dark-text-color: #d8d8d8;
+    --default-text-color: #d4d4d4;
+    --light-text-color: #888888;
+    --very-light-text-color: #666666;
+
+    --light-border-color: #2f2f2f;
+    --medium-border-color: #3f3f3f;
+    --dark-border-color: #888888;
+
+    --popuplar-kanji-text-color: #0275d8;
+
+    --pitch-accent-annotation-color: #ffffff;
+
+    --tag-text-color: #e1e1e1;
+    --tag-default-background-color: #69696e;
+    --tag-name-background-color: #489148;
+    --tag-expression-background-color: #b07f39;
+    --tag-popular-background-color: #025caa;
+    --tag-frequent-background-color: #4490a7;
+    --tag-archaism-background-color: #b04340;
+    --tag-dictionary-background-color: #9057ad;
+    --tag-frequency-background-color: #489148;
+    --tag-part-of-speech-background-color: #565656;
+    --tag-search-background-color: #69696e;
+    --tag-pitch-accent-dictionary-background-color: #6640be;
+}
+
 
 /*
  * Fonts
@@ -25,6 +91,7 @@
     src: url('/mixed/ttf/kanji-stroke-orders.ttf');
 }
 
+
 /*
  * General
  */
@@ -45,6 +112,8 @@ body {
     border: 0;
     padding: 0;
     overflow-y: scroll; /* always show scroll bar */
+    background-color: var(--background-color);
+    color: var(--default-text-color);
 }
 
 ol, ul {
@@ -68,10 +137,10 @@ h2 {
     font-size: 1.25em;
     font-weight: normal;
     margin: 0.25em 0 0;
-    border-bottom-width: 0.05714285714285714em; /* 14px * 1.25em => 1px */
-    border-bottom-style: solid;
+    border-bottom: 0.05714285714285714em solid var(--light-border-color); /* 14px * 1.25em => 1px */
 }
 
+
 /*
  * Navigation
  */
@@ -83,8 +152,8 @@ h2 {
     height: 2.1em;
     box-sizing: border-box;
     padding: 0.25em 0.5em;
-    border-bottom-width: 0.07142857em; /* 14px => 1px */
-    border-bottom-style: solid;
+    border-bottom: 0.07142857em solid var(--light-border-color); /* 14px => 1px */
+    background-color: var(--background-color);
     z-index: 10;
 }
 
@@ -131,6 +200,12 @@ h2 {
     user-select: none;
 }
 
+.icon-checkbox:checked+label {
+    /* Invert colors */
+    background-color: var(--default-text-color);
+    color: var(--background-color);
+}
+
 #query-parser-content {
     margin-top: 0.5em;
     font-size: 2em;
@@ -206,11 +281,21 @@ button.action-button {
 }
 
 .term-expression .kanji-link {
-    border-bottom-width: 0.03571428em; /* 28px => 1px */
-    border-bottom-style: dashed;
+    border-bottom: 0.03571428em dashed var(--dark-border-color); /* 28px => 1px */
+    color: var(--default-text-color);
     text-decoration: none;
 }
 
+.term-expression[data-frequency=popular]>.term-expression-text,
+.term-expression[data-frequency=popular]>.term-expression-text .kanji-link {
+    color: var(--popuplar-kanji-text-color);
+}
+
+.term-expression[data-frequency=rare]>.term-expression-text,
+.term-expression[data-frequency=rare]>.term-expression-text .kanji-link {
+    color: var(--very-light-text-color);
+}
+
 .entry:not(.entry-current) .current {
     display: none;
 }
@@ -225,6 +310,48 @@ button.action-button {
     white-space: nowrap;
     vertical-align: baseline;
     border-radius: 0.25em;
+    color: var(--tag-text-color);
+    background-color: var(--tag-default-background-color);
+}
+
+.tag[data-category=name] {
+    background-color: var(--tag-name-background-color);
+}
+
+.tag[data-category=expression] {
+    background-color: var(--tag-expression-background-color);
+}
+
+.tag[data-category=popular] {
+    background-color: var(--tag-popular-background-color);
+}
+
+.tag[data-category=frequent] {
+    background-color: var(--tag-frequent-background-color);
+}
+
+.tag[data-category=archaism] {
+    background-color: var(--tag-archaism-background-color);
+}
+
+.tag[data-category=dictionary] {
+    background-color: var(--tag-dictionary-background-color);
+}
+
+.tag[data-category=frequency] {
+    background-color: var(--tag-frequency-background-color);
+}
+
+.tag[data-category=partOfSpeech] {
+    background-color: var(--tag-part-of-speech-background-color);
+}
+
+.tag[data-category=search] {
+    background-color: var(--tag-search-background-color);
+}
+
+.tag[data-category=pitch-accent-dictionary] {
+    background-color: var(--tag-pitch-accent-dictionary-background-color);
 }
 
 .tag-inner {
@@ -249,8 +376,7 @@ button.action-button {
 }
 
 .entry+.entry {
-    border-top-width: 0.07142857em; /* 14px => 1px */
-    border-top-style: solid;
+    border-top: 0.07142857em solid var(--light-border-color); /* 14px => 1px */
 }
 
 .entry[data-type=term][data-expression-multi=true] .actions>.action-play-audio {
@@ -259,6 +385,7 @@ button.action-button {
 
 .term-reasons {
     display: inline-block;
+    color: var(--light-text-color);
 }
 
 .term-reasons>.term-reason+.term-reason-separator+.term-reason:before {
@@ -346,6 +473,7 @@ button.action-button {
     margin: 0;
     padding: 0;
     list-style-type: none;
+    color: var(--light-text-color);
 }
 
 .term-definition-list:not([data-count="0"]):not([data-count="1"]) {
@@ -364,6 +492,10 @@ button.action-button {
     list-style-type: circle;
 }
 
+.term-glossary {
+    color: var(--dark-text-color);
+}
+
 .term-definition-disambiguation-list[data-count="0"] {
     display: none;
 }
@@ -445,8 +577,7 @@ button.action-button {
 }
 
 .term-pitch-accent-container {
-    border-bottom-width: 0.05714285714285714em; /* 14px * 1.25em => 1px */
-    border-bottom-style: solid;
+    border-bottom: 0.05714285714285714em solid var(--light-border-color); /* 14px * 1.25em => 1px */
     padding-bottom: 0.25em;
     margin-bottom: 0.25em;
 }
@@ -455,6 +586,7 @@ button.action-button {
     margin: 0;
     padding: 0;
     list-style-type: none;
+    color: var(--light-text-color);
 }
 
 .term-pitch-accent-group-list:not([data-count="0"]):not([data-count="1"]) {
@@ -478,6 +610,7 @@ button.action-button {
 .term-pitch-accent {
     display: inline;
     line-height: 1.5em;
+    color: var(--dark-text-color);
 }
 
 .term-pitch-accent-list:not([data-count="0"]):not([data-count="1"])>.term-pitch-accent {
@@ -490,6 +623,7 @@ button.action-button {
 
 .term-pitch-accent-disambiguation-list {
     padding-right: 0.25em;
+    color: var(--light-text-color);
 }
 
 .term-pitch-accent-disambiguation-list:before {
@@ -522,6 +656,9 @@ button.action-button {
     display: inline-block;
     position: relative;
 }
+.term-pitch-accent-character:before {
+    border-color: var(--pitch-accent-annotation-color);
+}
 .term-pitch-accent-character[data-pitch='high']:before {
     content: "";
     display: block;
@@ -586,31 +723,36 @@ button.action-button {
 .term-pitch-accent-graph-line,
 .term-pitch-accent-graph-line-tail {
     fill: none;
-    stroke: #000000;
+    stroke: var(--pitch-accent-annotation-color);
     stroke-width: 5;
 }
 .term-pitch-accent-graph-line-tail {
     stroke-dasharray: 5 5;
 }
 #term-pitch-accent-graph-dot {
-    fill: #000000;
-    stroke: #000000;
+    fill: var(--pitch-accent-annotation-color);
+    stroke: var(--pitch-accent-annotation-color);
     stroke-width: 5;
 }
 #term-pitch-accent-graph-dot-downstep {
     fill: none;
-    stroke: #000000;
+    stroke: var(--pitch-accent-annotation-color);
     stroke-width: 5;
 }
 #term-pitch-accent-graph-dot-downstep>circle:last-of-type {
-    fill: #000000;
+    fill: var(--pitch-accent-annotation-color);
 }
 #term-pitch-accent-graph-triangle {
     fill: none;
-    stroke: #000000;
+    stroke: var(--pitch-accent-annotation-color);
     stroke-width: 5;
 }
 
+
+/*
+ * Glossary images
+ */
+
 .term-glossary-image-container {
     display: inline-block;
     white-space: nowrap;
@@ -620,6 +762,7 @@ button.action-button {
     line-height: 0;
     font-size: 0.07142857em; /* 14px => 1px */
     overflow: hidden;
+    background-color: var(--glossary-image-background-color);
 }
 
 .term-glossary-image-link {
@@ -642,6 +785,7 @@ button.action-button {
     display: table;
     table-layout: fixed;
     white-space: normal;
+    color: var(--light-text-color);
 }
 
 .term-glossary-item[data-has-image=true][data-image-load-state=load-error] .term-glossary-image-container-overlay:after {
@@ -746,8 +890,7 @@ button.action-button {
 }
 
 .kanji-glyph-data>tbody>tr>* {
-    border-top-width: 0.07142857em; /* 14px => 1px */
-    border-top-style: solid;
+    border-top: 0.07142857em solid var(--medium-border-color); /* 14px => 1px */
     text-align: left;
     vertical-align: top;
     padding: 0.36em;
@@ -783,9 +926,14 @@ button.action-button {
     margin: 0;
     padding: 0;
     list-style-type: none;
+    color: var(--light-text-color);
 }
 
 .kanji-glossary-list:not([data-count="0"]):not([data-count="1"]) {
     padding-left: 1.4em;
     list-style-type: decimal;
 }
+
+.kanji-glossary {
+    color: var(--dark-text-color);
+}