Adaptive custom themes (#416)

* feat: Smooth change in colour, no hard cut

Added option smoothing on colour change so there is no hard cut made when switching subjects

* feat: Themes can adapt to colour

* quick fix to forced mode as well

* [CodeFactor] Apply fixes

---------

Co-authored-by: codefactor-io <support@codefactor.io>

src/interface/pages/themeCreator.svelte

@@ -4,7 +4,10 @@
   import { slide } from 'svelte/transition';
   import { fade } from 'svelte/transition';
 
-  import { type LoadedCustomTheme } from '@/types/CustomThemes'
+  import {
+    type LoadedCustomTheme,
+    shouldForceThemeAppearance,
+  } from '@/types/CustomThemes'
 
   import { settingsState } from '@/seqta/utils/listeners/SettingsState'
 
@@ -40,7 +43,9 @@
     coverImage: null,
     isEditable: true,
     hideThemeName: false,
-    forceDark: undefined
+    forceTheme: undefined,
+    forceDark: undefined,
+    adaptiveCssVariables: [],
   })
   let closedAccordions = $state<string[]>([])
   let themeLoaded = $state(false);
@@ -80,7 +85,13 @@
         }))
       }
 
-      theme = loadedTheme
+      theme = {
+        ...loadedTheme,
+        adaptiveCssVariables: loadedTheme.adaptiveCssVariables ?? [],
+        forceTheme:
+          loadedTheme.forceTheme ??
+          (loadedTheme.forceDark !== undefined ? true : undefined),
+      }
       themeLoaded = true
     } else {
       themeLoaded = true
@@ -115,6 +126,13 @@
     }))
     themeClone.coverImage = theme.coverImage
 
+    if (shouldForceThemeAppearance(themeClone)) {
+      themeClone.forceTheme = true;
+    } else {
+      themeClone.forceTheme = false;
+      themeClone.forceDark = undefined;
+    }
+
     themeManager.clearPreview();
     await themeManager.saveTheme(themeClone);
     await themeManager.setTheme(themeClone.id);
@@ -317,6 +335,27 @@
 
     <Divider />
 
+    <div class="py-3">
+      <h2 class="text-sm font-bold">Adaptive CSS variables</h2>
+      <p class="text-xs text-zinc-600 dark:text-zinc-400">
+        One per line, each must start with <code class="text-xs">--</code>. These receive the same colour as the adaptive accent when &quot;Adaptive theme colour&quot; is enabled in general settings. Use them in Custom CSS, e.g. <code class="text-xs">border-color: var(--my-accent);</code>
+      </p>
+      <textarea
+        placeholder="--my-accent&#10;--class-banner"
+        value={theme.adaptiveCssVariables?.join('\n') ?? ''}
+        oninput={(e) => {
+          const lines = e.currentTarget.value
+            .split(/\r?\n/)
+            .map((s) => s.trim())
+            .filter(Boolean);
+          theme = { ...theme, adaptiveCssVariables: lines };
+        }}
+        class="p-2 mt-2 w-full min-h-[5rem] font-mono text-sm rounded-lg border-0 transition dark:placeholder-zinc-400 bg-zinc-200 dark:bg-zinc-700 focus:outline-none focus:ring-1 focus:ring-zinc-100 dark:focus:ring-zinc-700 focus:bg-zinc-300/50 dark:focus:bg-zinc-600"
+      ></textarea>
+    </div>
+
+    <Divider />
+
     {#each [
       {
         type: 'switch',
@@ -332,21 +371,28 @@
         title: 'Force Theme',
         description: 'Force users to use either dark or light mode',
         props: {
-          state: theme.forceDark !== undefined,
-          onChange: (value: boolean) => theme = { ...theme, forceDark: value ? false : undefined }
+          state: shouldForceThemeAppearance(theme),
+          onChange: (value: boolean) => {
+            if (value) {
+              theme = { ...theme, forceTheme: true, forceDark: false };
+            } else {
+              theme = { ...theme, forceTheme: false, forceDark: undefined };
+            }
+          }
         }
       },
       {
         type: 'conditional',
         props: {
-          condition: theme.forceDark !== undefined,
+          condition: shouldForceThemeAppearance(theme),
           children: {
             type: 'lightDarkToggle',
             title: 'Mode',
             description: 'Choose whether to force light or dark mode',
             props: {
               state: theme.forceDark === true,
-              onChange: (value: boolean) => theme = { ...theme, forceDark: value }
+              onChange: (value: boolean) =>
+                (theme = { ...theme, forceDark: value, forceTheme: true })
             }
           }
         }

src/plugins/built-in/themes/theme-manager.ts

@@ -1,8 +1,18 @@
 import localforage from "localforage";
 import browser from "webextension-polyfill";
-import type { CustomTheme, LoadedCustomTheme } from "@/types/CustomThemes";
+import {
+  type CustomTheme,
+  getForcedDarkMode,
+  type LoadedCustomTheme,
+  shouldForceThemeAppearance,
+} from "@/types/CustomThemes";
 import { settingsState } from "@/seqta/utils/listeners/SettingsState";
 import debounce from "@/seqta/utils/debounce";
+import { updateAllColors } from "@/seqta/ui/colors/Manager";
+import {
+  clearCustomThemeAdaptiveCssVariables,
+  setCustomThemeAdaptiveCssVariables,
+} from "@/seqta/ui/colors/customThemeAdaptiveBindings";
 
 type ThemeContent = {
   id: string;
@@ -14,6 +24,8 @@ type ThemeContent = {
   CustomCSS?: string;
   hideThemeName?: boolean;
   forceDark?: boolean;
+  forceTheme?: boolean;
+  adaptiveCssVariables?: string[];
   images: { id: string; variableName: string; data: string }[]; // data: base64
 };
 
@@ -209,7 +221,7 @@ export class ThemeManager {
         console.debug("[ThemeManager] Storing original settings");
         settingsState.originalSelectedColor = settingsState.selectedColor;
 
-        if (theme.forceDark) {
+        if (shouldForceThemeAppearance(theme)) {
           settingsState.originalDarkMode = settingsState.DarkMode;
         }
       }
@@ -240,6 +252,7 @@ export class ThemeManager {
         this.currentTheme = theme;
         settingsState.selectedTheme = themeId;
       }
+      void updateAllColors();
     } catch (error) {
       console.error("[ThemeManager] Error setting theme:", error);
     }
@@ -270,9 +283,10 @@ export class ThemeManager {
       }
 
       // Apply theme settings
-      if (theme.forceDark !== undefined) {
-        console.debug("[ThemeManager] Setting dark mode:", theme.forceDark);
-        settingsState.DarkMode = theme.forceDark;
+      if (shouldForceThemeAppearance(theme)) {
+        const dark = getForcedDarkMode(theme);
+        console.debug("[ThemeManager] Setting dark mode:", dark);
+        settingsState.DarkMode = dark;
       }
 
       // Use the stored selected color if available, otherwise use the default
@@ -289,6 +303,8 @@ export class ThemeManager {
         );
         settingsState.selectedColor = theme.defaultColour;
       }
+
+      setCustomThemeAdaptiveCssVariables(theme.adaptiveCssVariables ?? []);
     } catch (error) {
       console.error("[ThemeManager] Error applying theme:", error);
     }
@@ -373,6 +389,7 @@ export class ThemeManager {
       if (clearSelectedTheme) {
         settingsState.selectedTheme = "";
       }
+      clearCustomThemeAdaptiveCssVariables();
     } catch (error) {
       console.error("[ThemeManager] Error removing theme:", error);
     }
@@ -585,6 +602,13 @@ export class ThemeManager {
         isEditable: false,
         hideThemeName: themeData.hideThemeName ?? false,
         forceDark: themeData.forceDark,
+        forceTheme:
+          themeData.forceTheme !== undefined
+            ? themeData.forceTheme
+            : themeData.forceDark !== undefined
+              ? true
+              : undefined,
+        adaptiveCssVariables: themeData.adaptiveCssVariables,
       };
 
       await this.saveTheme(theme);
@@ -651,7 +675,7 @@ export class ThemeManager {
   public async previewTheme(theme: LoadedCustomTheme): Promise<void> {
     console.debug("[ThemeManager] Previewing theme:", theme.name);
     try {
-      const { CustomCSS, CustomImages, defaultColour, forceDark } = theme;
+      const { CustomCSS, CustomImages, defaultColour } = theme;
 
       // Store original settings only if this is a new theme
       if (!theme.webURL) {
@@ -697,13 +721,16 @@ export class ThemeManager {
       this.previousImageVariableNames = newImageVariableNames;
 
       // Apply theme settings
-      if (forceDark !== undefined) {
-        settingsState.DarkMode = forceDark;
+      if (shouldForceThemeAppearance(theme)) {
+        settingsState.DarkMode = getForcedDarkMode(theme);
       }
 
       if (defaultColour) {
         settingsState.selectedColor = defaultColour;
       }
+
+      setCustomThemeAdaptiveCssVariables(theme.adaptiveCssVariables ?? []);
+      void updateAllColors();
     } catch (error) {
       console.error("[ThemeManager] Error previewing theme:", error);
     }
@@ -769,15 +796,18 @@ export class ThemeManager {
         this.previousImageVariableNames = newImageVariableNames;
       }
 
-      // Always apply dark mode setting
-      if (theme.forceDark !== undefined) {
-        settingsState.DarkMode = theme.forceDark;
+      // Always apply dark mode setting when theme forces appearance
+      if (shouldForceThemeAppearance(theme as CustomTheme)) {
+        settingsState.DarkMode = getForcedDarkMode(theme as CustomTheme);
       }
 
       // Only apply color if this is a new theme
       if (!theme.webURL && theme.defaultColour) {
         settingsState.selectedColor = theme.defaultColour;
       }
+
+      setCustomThemeAdaptiveCssVariables(theme.adaptiveCssVariables ?? []);
+      void updateAllColors();
     } catch (error) {
       console.error("[ThemeManager] Error updating theme preview:", error);
     }
@@ -815,6 +845,8 @@ export class ThemeManager {
         this.previewStyleElement = null;
       }
 
+      clearCustomThemeAdaptiveCssVariables();
+
       // Restore original settings
       const storedColor = localStorage.getItem("originalPreviewColor");
 
@@ -844,6 +876,8 @@ export class ThemeManager {
         settingsState.DarkMode = this.originalPreviewTheme;
         this.originalPreviewTheme = null;
       }
+
+      void updateAllColors();
     } catch (error) {
       console.error("[ThemeManager] Error clearing preview:", error);
     }

src/seqta/ui/colors/Manager.ts

@@ -5,6 +5,7 @@ import { lightenAndPaleColor } from "./lightenAndPaleColor";
 import ColorLuminance from "./ColorLuminance";
 import { settingsState } from "@/seqta/utils/listeners/SettingsState";
 import { getAdaptiveColour } from "@/seqta/utils/adaptiveThemeColour";
+import { getCustomThemeAdaptiveCssVariables } from "@/seqta/ui/colors/customThemeAdaptiveBindings";
 
 import darkLogo from "@/resources/icons/betterseqta-light-full.png";
 import lightLogo from "@/resources/icons/betterseqta-dark-full.png";
@@ -127,6 +128,12 @@ function applyColorsWith(selectedColor: string) {
   // Apply all the properties
   applyProperties({ ...commonProps, ...modeProps, ...dynamicProps });
 
+  if (settingsState.selectedTheme) {
+    for (const name of getCustomThemeAdaptiveCssVariables()) {
+      setCSSVar(name, selectedColor);
+    }
+  }
+
   let alliframes = document.getElementsByTagName("iframe");
 
   for (let i = 0; i < alliframes.length; i++) {

src/seqta/ui/colors/customThemeAdaptiveBindings.ts

@@ -0,0 +1,40 @@
+/** Tracks which author-declared CSS variables mirror the effective accent; not persisted in settings storage. */
+
+const VALID_CUSTOM_PROP = /^--[a-zA-Z0-9_-]{1,120}$/;
+
+let boundNames: string[] = [];
+
+export function normalizeAdaptiveCssVariableNames(
+  names: string[] | undefined,
+): string[] {
+  if (!names?.length) return [];
+  const out: string[] = [];
+  const seen = new Set<string>();
+  for (const raw of names) {
+    const s = raw.trim();
+    if (!VALID_CUSTOM_PROP.test(s) || seen.has(s)) continue;
+    seen.add(s);
+    out.push(s);
+  }
+  return out;
+}
+
+export function setCustomThemeAdaptiveCssVariables(
+  names: string[] | undefined,
+): void {
+  for (const n of boundNames) {
+    document.documentElement.style.removeProperty(n);
+  }
+  boundNames = normalizeAdaptiveCssVariableNames(names);
+}
+
+export function getCustomThemeAdaptiveCssVariables(): string[] {
+  return boundNames;
+}
+
+export function clearCustomThemeAdaptiveCssVariables(): void {
+  for (const n of boundNames) {
+    document.documentElement.style.removeProperty(n);
+  }
+  boundNames = [];
+}

src/seqta/utils/listeners/StorageChanges.ts

@@ -20,6 +20,7 @@ export class StorageChangeHandler {
     settingsState.register("adaptiveThemeColourTransition", () =>
       void updateAllColors(),
     );
+    settingsState.register("selectedTheme", () => void updateAllColors());
     settingsState.register("DarkMode", this.handleDarkModeChange.bind(this));
     settingsState.register("onoff", this.handleOnOffChange.bind(this));
     settingsState.register("shortcuts", this.handleShortcutsChange.bind(this));

src/types/CustomThemes.ts

@@ -12,7 +12,14 @@ export type CustomTheme = {
   hideThemeName: boolean;
   webURL?: string;
   selectedColor?: string;
+  /**
+   * When true, the theme forces light/dark via `forceDark` (`false` = light, `true` = dark).
+   * When false/omitted, use legacy rule: `forceDark !== undefined` still means "force" for old JSON.
+   */
+  forceTheme?: boolean;
   forceDark?: boolean;
+  /** CSS custom property names (e.g. `--my-accent`) that receive the same value as `--better-main` when adaptive colours apply. */
+  adaptiveCssVariables?: string[];
 };
 
 export type LoadedCustomTheme = CustomTheme & {
@@ -37,3 +44,18 @@ export type ThemeList = {
   themes: CustomTheme[];
   selectedTheme: string;
 };
+
+/** Whether the theme forces appearance (light vs dark). */
+export function shouldForceThemeAppearance(theme: {
+  forceTheme?: boolean;
+  forceDark?: boolean;
+}): boolean {
+  if (theme.forceTheme === true) return true;
+  if (theme.forceTheme === false) return false;
+  return theme.forceDark !== undefined;
+}
+
+/** Resolved forced dark mode when forcing is active. */
+export function getForcedDarkMode(theme: { forceDark?: boolean }): boolean {
+  return theme.forceDark === true;
+}