diff --git a/src/librustdoc/html/render/context.rs b/src/librustdoc/html/render/context.rs
index 1030fe7474758..ed1eb66b97c36 100644
--- a/src/librustdoc/html/render/context.rs
+++ b/src/librustdoc/html/render/context.rs
@@ -647,11 +647,35 @@ impl<'tcx> FormatRenderer<'tcx> for Context<'tcx> {
                      </noscript>\
                      <link rel=\"stylesheet\" \
                          href=\"{static_root_path}{settings_css}\">\
-                     <script defer src=\"{static_root_path}{settings_js}\"></script>",
+                     <script defer src=\"{static_root_path}{settings_js}\"></script>\
+                     <link rel=\"preload\" href=\"{static_root_path}{theme_light_css}\" \
+                         as=\"style\">\
+                     <link rel=\"preload\" href=\"{static_root_path}{theme_dark_css}\" \
+                         as=\"style\">\
+                     <link rel=\"preload\" href=\"{static_root_path}{theme_ayu_css}\" \
+                         as=\"style\">",
                     static_root_path = page.get_static_root_path(),
                     settings_css = static_files::STATIC_FILES.settings_css,
                     settings_js = static_files::STATIC_FILES.settings_js,
-                )
+                    theme_light_css = static_files::STATIC_FILES.theme_light_css,
+                    theme_dark_css = static_files::STATIC_FILES.theme_dark_css,
+                    theme_ayu_css = static_files::STATIC_FILES.theme_ayu_css,
+                );
+                // Pre-load all theme CSS files, so that switching feels seamless.
+                //
+                // When loading settings.html as a popover, the equivalent HTML is
+                // generated in main.js.
+                for file in &shared.style_files {
+                    if let Ok(theme) = file.basename() {
+                        write!(
+                            buf,
+                            "<link rel=\"preload\" href=\"{root_path}{theme}{suffix}.css\" \
+                                as=\"style\">",
+                            root_path = page.static_root_path.unwrap_or(""),
+                            suffix = page.resource_suffix,
+                        );
+                    }
+                }
             },
             &shared.style_files,
         );
diff --git a/src/librustdoc/html/static/js/main.js b/src/librustdoc/html/static/js/main.js
index 5e8c0e8d10c22..403b5004d6558 100644
--- a/src/librustdoc/html/static/js/main.js
+++ b/src/librustdoc/html/static/js/main.js
@@ -1,20 +1,9 @@
 // Local js definitions:
 /* global addClass, getSettingValue, hasClass, searchState */
-/* global onEach, onEachLazy, removeClass */
+/* global onEach, onEachLazy, removeClass, getVar */
 
 "use strict";
 
-// Get a value from the rustdoc-vars div, which is used to convey data from
-// Rust to the JS. If there is no such element, return null.
-function getVar(name) {
-    const el = document.getElementById("rustdoc-vars");
-    if (el) {
-        return el.attributes["data-" + name].value;
-    } else {
-        return null;
-    }
-}
-
 // 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) {
@@ -187,6 +176,15 @@ function loadCss(cssUrl) {
     document.getElementsByTagName("head")[0].appendChild(link);
 }
 
+function preLoadCss(cssUrl) {
+    // https://developer.mozilla.org/en-US/docs/Web/HTML/Link_types/preload
+    const link = document.createElement("link");
+    link.href = cssUrl;
+    link.rel = "preload";
+    link.as = "style";
+    document.getElementsByTagName("head")[0].appendChild(link);
+}
+
 (function() {
     const isHelpPage = window.location.pathname.endsWith("/help.html");
 
@@ -207,6 +205,23 @@ function loadCss(cssUrl) {
         // hopefully be loaded when the JS will generate the settings content.
         loadCss(getVar("static-root-path") + getVar("settings-css"));
         loadScript(getVar("static-root-path") + getVar("settings-js"));
+        preLoadCss(getVar("static-root-path") + getVar("theme-light-css"));
+        preLoadCss(getVar("static-root-path") + getVar("theme-dark-css"));
+        preLoadCss(getVar("static-root-path") + getVar("theme-ayu-css"));
+        // Pre-load all theme CSS files, so that switching feels seamless.
+        //
+        // When loading settings.html as a standalone page, the equivalent HTML is
+        // generated in context.rs.
+        setTimeout(() => {
+            const themes = getVar("themes").split(",");
+            for (const theme of themes) {
+                // if there are no themes, do nothing
+                // "".split(",") == [""]
+                if (theme !== "") {
+                    preLoadCss(getVar("root-path") + theme + ".css");
+                }
+            }
+        }, 0);
     };
 
     window.searchState = {
diff --git a/src/librustdoc/html/static/js/storage.js b/src/librustdoc/html/static/js/storage.js
index c72ac254fc08c..c3fed9a72d4e2 100644
--- a/src/librustdoc/html/static/js/storage.js
+++ b/src/librustdoc/html/static/js/storage.js
@@ -7,7 +7,6 @@
 
 const darkThemes = ["dark", "ayu"];
 window.currentTheme = document.getElementById("themeStyle");
-window.mainTheme = document.getElementById("mainThemeStyle");
 
 // WARNING: RUSTDOC_MOBILE_BREAKPOINT MEDIA QUERY
 // If you update this line, then you also need to update the media query with the same
@@ -44,8 +43,6 @@ function getSettingValue(settingName) {
 
 const localStoredTheme = getSettingValue("theme");
 
-const savedHref = [];
-
 // eslint-disable-next-line no-unused-vars
 function hasClass(elem, className) {
     return elem && elem.classList && elem.classList.contains(className);
@@ -102,6 +99,7 @@ function onEach(arr, func, reversed) {
  * @param {function(?)}                   func       - The callback
  * @param {boolean}                       [reversed] - Whether to iterate in reverse
  */
+// eslint-disable-next-line no-unused-vars
 function onEachLazy(lazyArray, func, reversed) {
     return onEach(
         Array.prototype.slice.call(lazyArray),
@@ -125,30 +123,37 @@ function getCurrentValue(name) {
     }
 }
 
-function switchTheme(styleElem, mainStyleElem, newThemeName, saveTheme) {
+// Get a value from the rustdoc-vars div, which is used to convey data from
+// 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;
+    }
+});
+
+function switchTheme(newThemeName, saveTheme) {
     // If this new value comes from a system setting or from the previously
     // saved theme, no need to save it.
     if (saveTheme) {
         updateLocalStorage("theme", newThemeName);
     }
 
-    if (savedHref.length === 0) {
-        onEachLazy(document.getElementsByTagName("link"), el => {
-            savedHref.push(el.href);
-        });
+    let newHref;
+
+    if (newThemeName === "light" || newThemeName === "dark" || newThemeName === "ayu") {
+        newHref = getVar("static-root-path") + getVar("theme-" + newThemeName + "-css");
+    } else {
+        newHref = getVar("root-path") + newThemeName + getVar("resource-suffix") + ".css";
     }
-    const newHref = savedHref.find(url => {
-        const m = url.match(/static\.files\/(.*)-[a-f0-9]{16}\.css$/);
-        if (m && m[1] === newThemeName) {
-            return true;
-        }
-        const m2 = url.match(/\/([^/]*)\.css$/);
-        if (m2 && m2[1].startsWith(newThemeName)) {
-            return true;
-        }
-    });
-    if (newHref && newHref !== styleElem.href) {
-        styleElem.href = newHref;
+
+    if (!window.currentTheme) {
+        document.write(`<link rel="stylesheet" id="themeStyle" href="${newHref}">`);
+        window.currentTheme = document.getElementById("themeStyle");
+    } else if (newHref !== window.currentTheme.href) {
+        window.currentTheme.href = newHref;
     }
 }
 
@@ -164,7 +169,7 @@ const updateTheme = (function() {
      */
     function updateTheme() {
         const use = (theme, saveTheme) => {
-            switchTheme(window.currentTheme, window.mainTheme, theme, saveTheme);
+            switchTheme(theme, saveTheme);
         };
 
         // maybe the user has disabled the setting in the meantime!
diff --git a/src/librustdoc/html/templates/page.html b/src/librustdoc/html/templates/page.html
index e896850fab6bd..532660e3d33c7 100644
--- a/src/librustdoc/html/templates/page.html
+++ b/src/librustdoc/html/templates/page.html
@@ -17,12 +17,6 @@
     <link rel="stylesheet" {#+ #}
           href="{{static_root_path|safe}}{{files.rustdoc_css}}" {#+ #}
           id="mainThemeStyle"> {# #}
-    <link rel="stylesheet" id="themeStyle" href="{{static_root_path|safe}}{{files.theme_light_css}}"> {# #}
-    <link rel="stylesheet" disabled href="{{static_root_path|safe}}{{files.theme_dark_css}}"> {# #}
-    <link rel="stylesheet" disabled href="{{static_root_path|safe}}{{files.theme_ayu_css}}"> {# #}
-    {% for theme in themes %}
-        <link rel="stylesheet" disabled href="{{page.root_path|safe}}{{theme}}{{page.resource_suffix}}.css"> {# #}
-    {% endfor %}
     {% if !layout.default_settings.is_empty() %}
     <script id="default-settings" {#+ #}
       {%~ for (k, v) in layout.default_settings ~%}
@@ -30,6 +24,21 @@
       {% endfor %}
     ></script> {# #}
     {% endif %}
+    <div id="rustdoc-vars" {#+ #}
+         data-root-path="{{page.root_path|safe}}" {#+ #}
+         data-static-root-path="{{static_root_path|safe}}" {#+ #}
+         data-current-crate="{{layout.krate}}" {#+ #}
+         data-themes="{{themes|join(",") }}" {#+ #}
+         data-resource-suffix="{{page.resource_suffix}}" {#+ #}
+         data-rustdoc-version="{{rustdoc_version}}" {#+ #}
+         data-search-js="{{files.search_js}}" {#+ #}
+         data-settings-js="{{files.settings_js}}" {#+ #}
+         data-settings-css="{{files.settings_css}}" {#+ #}
+         data-theme-light-css="{{files.theme_light_css}}" {#+ #}
+         data-theme-dark-css="{{files.theme_dark_css}}" {#+ #}
+         data-theme-ayu-css="{{files.theme_ayu_css}}" {#+ #}
+    > {# #}
+    </div> {# #}
     <script src="{{static_root_path|safe}}{{files.storage_js}}"></script> {# #}
     {% if page.css_class.contains("crate") %}
     <script defer src="{{page.root_path|safe}}crates{{page.resource_suffix}}.js"></script> {# #}
@@ -44,6 +53,12 @@
     <script defer src="{{static_root_path|safe}}{{files.scrape_examples_js}}"></script> {# #}
     {% endif %}
     <noscript> {# #}
+        <link rel="stylesheet" {#+ #}
+           media="(prefers-color-scheme:light)" {#+ #}
+           href="{{static_root_path|safe}}{{files.theme_light_css}}"> {# #}
+        <link rel="stylesheet" {#+ #}
+           media="(prefers-color-scheme:dark)" {#+ #}
+           href="{{static_root_path|safe}}{{files.theme_dark_css}}"> {# #}
         <link rel="stylesheet" {#+ #}
            href="{{static_root_path|safe}}{{files.noscript_css}}"> {# #}
     </noscript> {# #}
@@ -132,17 +147,5 @@ <h2></h2> {# #}
         {% if page.css_class != "source" %}</div>{% endif %}
     </main> {# #}
     {{ layout.external_html.after_content|safe }}
-    <div id="rustdoc-vars" {#+ #}
-         data-root-path="{{page.root_path|safe}}" {#+ #}
-         data-static-root-path="{{static_root_path|safe}}" {#+ #}
-         data-current-crate="{{layout.krate}}" {#+ #}
-         data-themes="{{themes|join(",") }}" {#+ #}
-         data-resource-suffix="{{page.resource_suffix}}" {#+ #}
-         data-rustdoc-version="{{rustdoc_version}}" {#+ #}
-         data-search-js="{{files.search_js}}" {#+ #}
-         data-settings-js="{{files.settings_js}}" {#+ #}
-         data-settings-css="{{files.settings_css}}" {#+ #}
-    > {# #}
-    </div> {# #}
 </body> {# #}
 </html> {# #}
diff --git a/tests/run-make-fulldeps/rustdoc-themes/foo.rs b/tests/run-make-fulldeps/rustdoc-themes/foo.rs
index 58efaf7d5a05a..995544aeff998 100644
--- a/tests/run-make-fulldeps/rustdoc-themes/foo.rs
+++ b/tests/run-make-fulldeps/rustdoc-themes/foo.rs
@@ -1,4 +1,4 @@
 // @has test.css
 // @has foo/struct.Foo.html
-// @has - '//link[@rel="stylesheet"]/@href' '../test.css'
+// @has - '//*[@id="rustdoc-vars"]/@data-themes' 'test'
 pub struct Foo;
diff --git a/tests/rustdoc-gui/scrape-examples-button-focus.goml b/tests/rustdoc-gui/scrape-examples-button-focus.goml
index 1b5c3a0d202a0..16f0ced8c6eaa 100644
--- a/tests/rustdoc-gui/scrape-examples-button-focus.goml
+++ b/tests/rustdoc-gui/scrape-examples-button-focus.goml
@@ -8,24 +8,24 @@ focus: ".scraped-example-list > .scraped-example .next"
 press-key: "Enter"
 assert-property-false: (".scraped-example-list > .scraped-example pre", {
     "scrollTop": |initialScrollTop|
-})
+}, NEAR)
 focus: ".scraped-example-list > .scraped-example .prev"
 press-key: "Enter"
 assert-property: (".scraped-example-list > .scraped-example pre", {
     "scrollTop": |initialScrollTop|
-})
+}, NEAR)
 
 // The expand button increases the scrollHeight of the minimized code viewport
 store-property: (smallOffsetHeight, ".scraped-example-list > .scraped-example pre", "offsetHeight")
 assert-property-false: (".scraped-example-list > .scraped-example pre", {
     "scrollHeight": |smallOffsetHeight|
-})
+}, NEAR)
 focus: ".scraped-example-list > .scraped-example .expand"
 press-key: "Enter"
 assert-property-false: (".scraped-example-list > .scraped-example pre", {
     "offsetHeight": |smallOffsetHeight|
-})
+}, NEAR)
 store-property: (fullOffsetHeight, ".scraped-example-list > .scraped-example pre", "offsetHeight")
 assert-property: (".scraped-example-list > .scraped-example pre", {
     "scrollHeight": |fullOffsetHeight|
-})
+}, NEAR)