diff --git a/ext/bg/js/options.js b/ext/bg/js/options.js
index 088945c0..cadc4443 100644
--- a/ext/bg/js/options.js
+++ b/ext/bg/js/options.js
@@ -277,6 +277,7 @@ function profileOptionsCreateDefaults() {
             compactGlossaries: false,
             mainDictionary: '',
             popupTheme: 'default',
+            popupOuterTheme: 'default',
             customPopupCss: ''
         },
 
diff --git a/ext/bg/js/settings-popup-preview.js b/ext/bg/js/settings-popup-preview.js
index 6f64c240..53a5f1d0 100644
--- a/ext/bg/js/settings-popup-preview.js
+++ b/ext/bg/js/settings-popup-preview.js
@@ -22,6 +22,7 @@ class SettingsPopupPreview {
         this.frontend = null;
         this.apiOptionsGetOld = apiOptionsGet;
         this.popupShown = false;
+        this.themeChangeTimeout = null;
     }
 
     static create() {
@@ -97,6 +98,13 @@ class SettingsPopupPreview {
 
     onThemeDarkCheckboxChanged(node) {
         document.documentElement.classList.toggle('dark', node.checked);
+        if (this.themeChangeTimeout !== null) {
+            clearTimeout(this.themeChangeTimeout);
+        }
+        this.themeChangeTimeout = setTimeout(() => {
+            this.themeChangeTimeout = null;
+            this.frontend.popup.updateTheme();
+        }, 300);
     }
 
     setText(text) {
diff --git a/ext/bg/js/settings.js b/ext/bg/js/settings.js
index b98754ab..900b89bb 100644
--- a/ext/bg/js/settings.js
+++ b/ext/bg/js/settings.js
@@ -40,6 +40,7 @@ async function formRead(options) {
     options.general.popupHorizontalOffset2 = parseInt($('#popup-horizontal-offset2').val(), 0);
     options.general.popupVerticalOffset2 = parseInt($('#popup-vertical-offset2').val(), 10);
     options.general.popupTheme = $('#popup-theme').val();
+    options.general.popupOuterTheme = $('#popup-outer-theme').val();
     options.general.customPopupCss = $('#custom-popup-css').val();
 
     options.audio.enabled = $('#audio-playback-enabled').prop('checked');
@@ -109,6 +110,7 @@ async function formWrite(options) {
     $('#popup-horizontal-offset2').val(options.general.popupHorizontalOffset2);
     $('#popup-vertical-offset2').val(options.general.popupVerticalOffset2);
     $('#popup-theme').val(options.general.popupTheme);
+    $('#popup-outer-theme').val(options.general.popupOuterTheme);
     $('#custom-popup-css').val(options.general.customPopupCss);
 
     $('#audio-playback-enabled').prop('checked', options.audio.enabled);
diff --git a/ext/bg/settings.html b/ext/bg/settings.html
index 531c0e86..08e56a09 100644
--- a/ext/bg/settings.html
+++ b/ext/bg/settings.html
@@ -232,11 +232,23 @@
                 </div>
 
                 <div class="form-group">
-                    <label for="popup-theme">Theme</label>
-                    <select class="form-control" id="popup-theme">
-                        <option value="default">Light</option>
-                        <option value="dark">Dark</option>
-                    </select>
+                    <div class="row">
+                        <div class="col-xs-6">
+                            <label for="popup-theme">Popup theme</label>
+                            <select class="form-control" id="popup-theme">
+                                <option value="default">Light</option>
+                                <option value="dark">Dark</option>
+                            </select>
+                        </div>
+                        <div class="col-xs-6">
+                            <label for="popup-outer-theme">Popup shadow theme</label>
+                            <select class="form-control" id="popup-outer-theme">
+                                <option value="auto">Auto-detect</option>
+                                <option value="default">Light</option>
+                                <option value="dark">Dark</option>
+                            </select>
+                        </div>
+                    </div>
                 </div>
 
                 <div class="form-group options-advanced">
diff --git a/ext/fg/js/popup.js b/ext/fg/js/popup.js
index 5ca8643f..ef4cdb67 100644
--- a/ext/fg/js/popup.js
+++ b/ext/fg/js/popup.js
@@ -85,7 +85,7 @@ class Popup {
 
     async setOptions(options) {
         this.options = options;
-        this.container.dataset.yomichanTheme = options.general.popupTheme;
+        this.updateTheme();
     }
 
     async show(elementRect, writingMode) {
@@ -270,6 +270,47 @@ class Popup {
         }
     }
 
+    updateTheme() {
+        this.container.dataset.yomichanTheme = this.getTheme(this.options.general.popupOuterTheme);
+    }
+
+    getTheme(themeName) {
+        if (themeName === 'auto') {
+            const color = [255, 255, 255];
+            Popup.addColor(color, Popup.getColorInfo(window.getComputedStyle(document.documentElement).backgroundColor));
+            Popup.addColor(color, Popup.getColorInfo(window.getComputedStyle(document.body).backgroundColor));
+            const dark = (color[0] < 128 && color[1] < 128 && color[2] < 128);
+            themeName = dark ? 'dark' : 'default';
+        }
+
+        return themeName;
+    }
+
+    static addColor(target, color) {
+        if (color === null) { return; }
+
+        const a = color[3];
+        if (a <= 0.0) { return; }
+
+        const aInv = 1.0 - a;
+        for (let i = 0; i < 3; ++i) {
+            target[i] = target[i] * aInv + color[i] * a;
+        }
+    }
+
+    static getColorInfo(cssColor) {
+        const m = /^\s*rgba?\s*\(\s*(\d+)\s*,\s*(\d+)\s*,\s*(\d+)\s*(?:,\s*([\d\.]+)\s*)?\)\s*$/.exec(cssColor);
+        if (m === null) { return null; }
+
+        const m4 = m[4];
+        return [
+            Number.parseInt(m[1], 10),
+            Number.parseInt(m[2], 10),
+            Number.parseInt(m[3], 10),
+            m4 ? Math.max(0.0, Math.min(1.0, Number.parseFloat(m4))) : 1.0
+        ];
+    }
+
     async containsPoint(x, y) {
         for (let popup = this; popup !== null && popup.isVisible(); popup = popup.child) {
             const rect = popup.container.getBoundingClientRect();