(core) Add dark mode to user preferences

Summary:
Adds initial implementation of dark mode. Preferences for dark mode are
available on the account settings page. Dark mode is currently a beta feature
as there are still some small bugs to squash and a few remaining UI elements
to style.

Test Plan: Browser tests.

Reviewers: jarek

Reviewed By: jarek

Subscribers: paulfitz, jarek

Differential Revision: https://phab.getgrist.com/D3587

app/client/lib/ACSelect.ts

@@ -1,6 +1,6 @@
 import {ACIndex, ACItem, buildHighlightedDom} from 'app/client/lib/ACIndex';
 import {Autocomplete, IAutocompleteOptions} from 'app/client/lib/autocomplete';
-import {colors} from "app/client/ui2018/cssVars";
+import {theme} from "app/client/ui2018/cssVars";
 import {icon} from "app/client/ui2018/icons";
 import {menuCssClass} from 'app/client/ui2018/menus';
 import {dom, DomElementArg, Holder, IDisposableOwner, Observable, styled} from 'grainjs';
@@ -96,11 +96,12 @@ const cssSelectBtn = styled('div', `
   position: relative;
   width: 100%;
   height: 30px;
-  color: ${colors.dark};
-  --icon-color: ${colors.dark};
+  color: ${theme.selectButtonFg};
+  --icon-color: ${theme.selectButtonFg};
 `);
 
 const cssSelectItem = styled('li', `
+  color: ${theme.menuItemFg};
   display: block;
   white-space: pre;
   overflow: hidden;
@@ -110,12 +111,14 @@ const cssSelectItem = styled('li', `
   cursor: pointer;
 
   &.selected {
-    background-color: var(--weaseljs-selected-background-color, #5AC09C);
-    color:            var(--weaseljs-selected-color, white);
+    background-color: ${theme.menuItemSelectedBg};
+    color:            ${theme.menuItemSelectedFg};
   }
 `);
 
 const cssInput = styled('input', `
+  color: ${theme.inputFg};
+  background-color: ${theme.inputBg};
   appearance: none;
   -webkit-appearance: none;
   -moz-appearance: none;
@@ -123,20 +126,23 @@ const cssInput = styled('input', `
   width: 100%;
   padding: 0 6px;
   outline: none;
-  border: 1px solid ${colors.darkGrey};
+  border: 1px solid ${theme.inputBorder};
   border-radius: 3px;
   cursor: pointer;
   line-height: 16px;
   cursor: pointer;
 
   &:disabled {
-    color: grey;
-    background-color: initial;
+    color: ${theme.inputDisabledFg};
+    background-color: ${theme.inputDisabledBg};
   }
   &:focus {
     cursor: initial;
     outline: none;
-    box-shadow: 0px 0px 2px 2px #5E9ED6;
+    box-shadow: 0px 0px 2px 2px ${theme.inputFocus};
+  }
+  &::placeholder {
+    color: ${theme.inputPlaceholderFg};
   }
 `);
 
@@ -147,8 +153,8 @@ const cssIcon = styled(icon, `
 `);
 
 const cssMatchText = styled('span', `
-  color: ${colors.lightGreen};
+  color: ${theme.autocompleteMatchText};
   .selected > & {
-    color: ${colors.lighterGreen};
+    color: ${theme.autocompleteSelectedMatchText};
   }
 `);

app/client/lib/TokenField.ts

@@ -18,7 +18,7 @@
 import { ACItem } from 'app/client/lib/ACIndex';
 import { modKeyProp } from 'app/client/lib/browserInfo';
 import { Autocomplete, IAutocompleteOptions } from 'app/client/lib/autocomplete';
-import { colors, testId } from 'app/client/ui2018/cssVars';
+import { colors, testId, theme } from 'app/client/ui2018/cssVars';
 import { icon } from 'app/client/ui2018/icons';
 import { csvDecodeRow, csvEncodeRow } from 'app/common/csvFormat';
 import { computedArray, IDisposableCtor, IObsArraySplice, ObsArray, obsArray, Observable } from 'grainjs';
@@ -679,6 +679,8 @@ const cssInputWrapper = styled('div', `
 `);
 
 const cssTokenInput = styled('input', `
+  color: ${theme.cellEditorFg};
+  background-color: ${theme.cellEditorBg};
   flex: auto;
   -webkit-appearance: none;
   -moz-appearance: none;

app/client/lib/Validator.ts

@@ -1,5 +1,5 @@
+import { theme } from 'app/client/ui2018/cssVars';
 import { Disposable, dom, Observable, styled } from 'grainjs';
-import { colors } from 'app/client/ui2018/cssVars';
 
 /**
  * Simple validation controls. Renders as a red text with a validation message.
@@ -117,5 +117,5 @@ export class Validator extends Disposable {
 }
 
 const cssError = styled('div.validator', `
-  color: ${colors.error};
+  color: ${theme.errorText};
 `);

app/client/lib/koForm.css

@@ -103,7 +103,7 @@ div:hover > .kf_tooltip {
   min-width: 16px;
   min-height: 16px;
   padding: 4px;
-  background-color: white;
+  background-color: var(--grist-theme-popup-bg, white);
   border-radius: 2px;
   box-shadow: 0 1px 1px 1px rgba(0,0,0,0.15);
   line-height: 1.1rem;
@@ -129,7 +129,7 @@ div:hover > .kf_tooltip {
   right: 20px;
   width: 10px;
   height: 10px;
-  background-color: white;
+  background-color: var(--grist-theme-popup-bg, white);
   transform: rotate(45deg);
   z-index: 11;
 }
@@ -393,6 +393,7 @@ div:hover > .kf_tooltip {
 }
 
 .kf_label {
+  color: var(--grist-theme-text, unset);
   white-space: nowrap;
   font-size: 1.1rem;
   cursor: default;
@@ -436,7 +437,7 @@ div:hover > .kf_tooltip {
   top: 0;
   left: 0;
   padding: 0;
-  color: #333;
+  color: var(--grist-theme-input-fg, #333);
 }
 
 .elabel_content_measure {