diff --git a/src/librustdoc/html/static/css/rustdoc.css b/src/librustdoc/html/static/css/rustdoc.css
index 7d578b5c7754a..933a44c5aa78d 100644
--- a/src/librustdoc/html/static/css/rustdoc.css
+++ b/src/librustdoc/html/static/css/rustdoc.css
@@ -87,21 +87,6 @@
 	box-sizing: border-box;
 }
 
-/* This part handles the "default" theme being used depending on the system one. */
-html {
-	content: "";
-}
-@media (prefers-color-scheme: light) {
-	html {
-		content: "light";
-	}
-}
-@media (prefers-color-scheme: dark) {
-	html {
-		content: "dark";
-	}
-}
-
 /* General structure and fonts */
 
 body {
@@ -1538,7 +1523,7 @@ However, it's not needed with smaller screen width because the doc/code block is
 /*
 WARNING: RUSTDOC_MOBILE_BREAKPOINT MEDIA QUERY
 If you update this line, then you also need to update the line with the same warning
-in storage.js
+in main.js
 */
 @media (max-width: 700px) {
 	/* When linking to an item with an `id` (for instance, by clicking a link in the sidebar,
diff --git a/src/librustdoc/html/static/js/main.js b/src/librustdoc/html/static/js/main.js
index 403b5004d6558..1487ebf9b0aa1 100644
--- a/src/librustdoc/html/static/js/main.js
+++ b/src/librustdoc/html/static/js/main.js
@@ -4,6 +4,11 @@
 
 "use strict";
 
+// WARNING: RUSTDOC_MOBILE_BREAKPOINT MEDIA QUERY
+// If you update this line, then you also need to update the media query with the same
+// warning in rustdoc.css
+window.RUSTDOC_MOBILE_BREAKPOINT = 700;
+
 // Given a basename (e.g. "storage") and an extension (e.g. ".js"), return a URL
 // for a resource under the root-path, with the resource-suffix.
 function resourcePath(basename, extension) {
diff --git a/src/librustdoc/html/static/js/storage.js b/src/librustdoc/html/static/js/storage.js
index c3fed9a72d4e2..8d82b5b78edbb 100644
--- a/src/librustdoc/html/static/js/storage.js
+++ b/src/librustdoc/html/static/js/storage.js
@@ -8,29 +8,14 @@
 const darkThemes = ["dark", "ayu"];
 window.currentTheme = document.getElementById("themeStyle");
 
-// WARNING: RUSTDOC_MOBILE_BREAKPOINT MEDIA QUERY
-// If you update this line, then you also need to update the media query with the same
-// warning in rustdoc.css
-window.RUSTDOC_MOBILE_BREAKPOINT = 700;
-
 const settingsDataset = (function() {
     const settingsElement = document.getElementById("default-settings");
-    if (settingsElement === null) {
-        return null;
-    }
-    const dataset = settingsElement.dataset;
-    if (dataset === undefined) {
-        return null;
-    }
-    return dataset;
+    return settingsElement && settingsElement.dataset ? settingsElement.dataset : null;
 })();
 
 function getSettingValue(settingName) {
     const current = getCurrentValue(settingName);
-    if (current !== null) {
-        return current;
-    }
-    if (settingsDataset !== null) {
+    if (current === null && settingsDataset !== null) {
         // See the comment for `default_settings.into_iter()` etc. in
         // `Options::from_matches` in `librustdoc/config.rs`.
         const def = settingsDataset[settingName.replace(/-/g,"_")];
@@ -38,7 +23,7 @@ function getSettingValue(settingName) {
             return def;
         }
     }
-    return null;
+    return current;
 }
 
 const localStoredTheme = getSettingValue("theme");
@@ -49,18 +34,16 @@ function hasClass(elem, className) {
 }
 
 function addClass(elem, className) {
-    if (!elem || !elem.classList) {
-        return;
+    if (elem && elem.classList) {
+        elem.classList.add(className);
     }
-    elem.classList.add(className);
 }
 
 // eslint-disable-next-line no-unused-vars
 function removeClass(elem, className) {
-    if (!elem || !elem.classList) {
-        return;
+    if (elem && elem.classList) {
+        elem.classList.remove(className);
     }
-    elem.classList.remove(className);
 }
 
 /**
@@ -127,11 +110,7 @@ function getCurrentValue(name) {
 // Rust to the JS. If there is no such element, return null.
 const getVar = (function getVar(name) {
     const el = document.getElementById("rustdoc-vars");
-    if (el) {
-        return el.attributes["data-" + name].value;
-    } else {
-        return null;
-    }
+    return el ? el.attributes["data-" + name].value : null;
 });
 
 function switchTheme(newThemeName, saveTheme) {
@@ -158,6 +137,9 @@ function switchTheme(newThemeName, saveTheme) {
 }
 
 const updateTheme = (function() {
+    // only listen to (prefers-color-scheme: dark) because light is the default
+    const mql = window.matchMedia("(prefers-color-scheme: dark)");
+
     /**
      * Update the current theme to match whatever the current combination of
      * * the preference for using the system theme
@@ -177,7 +159,7 @@ const updateTheme = (function() {
             const lightTheme = getSettingValue("preferred-light-theme") || "light";
             const darkTheme = getSettingValue("preferred-dark-theme") || "dark";
 
-            if (isDarkMode()) {
+            if (mql.matches) {
                 use(darkTheme, true);
             } else {
                 // prefers a light theme, or has no preference
@@ -191,37 +173,7 @@ const updateTheme = (function() {
         }
     }
 
-    // This is always updated below to a function () => bool.
-    let isDarkMode;
-
-    // Determine the function for isDarkMode, and if we have
-    // `window.matchMedia`, set up an event listener on the preferred color
-    // scheme.
-    //
-    // Otherwise, fall back to the prefers-color-scheme value CSS captured in
-    // the "content" property.
-    if (window.matchMedia) {
-        // only listen to (prefers-color-scheme: dark) because light is the default
-        const mql = window.matchMedia("(prefers-color-scheme: dark)");
-
-        isDarkMode = () => mql.matches;
-
-        if (mql.addEventListener) {
-            mql.addEventListener("change", updateTheme);
-        } else {
-            // This is deprecated, see:
-            // https://developer.mozilla.org/en-US/docs/Web/API/MediaQueryList/addListener
-            mql.addListener(updateTheme);
-        }
-    } else {
-        // fallback to the CSS computed value
-        const cssContent = getComputedStyle(document.documentElement)
-            .getPropertyValue("content");
-        // (Note: the double-quotes come from that this is a CSS value, which
-        // might be a length, string, etc.)
-        const cssColorScheme = cssContent || "\"light\"";
-        isDarkMode = () => (cssColorScheme === "\"dark\"");
-    }
+    mql.addEventListener("change", updateTheme);
 
     return updateTheme;
 })();