diff --git a/src/public/app/layouts/desktop_layout.js b/src/public/app/layouts/desktop_layout.js
index fc06413d44..08e1f1e439 100644
--- a/src/public/app/layouts/desktop_layout.js
+++ b/src/public/app/layouts/desktop_layout.js
@@ -46,6 +46,7 @@ import OpenNoteButtonWidget from "../widgets/buttons/open_note_button_widget.js"
 import MermaidWidget from "../widgets/mermaid.js";
 import BookmarkButtons from "../widgets/bookmark_buttons.js";
 import NoteWrapperWidget from "../widgets/note_wrapper.js";
+import BannerMessageWidget from "../widgets/banner_message.js";
 
 export default class DesktopLayout {
     constructor(customWidgets) {
@@ -57,6 +58,7 @@ export default class DesktopLayout {
 
         return new RootContainer()
             .setParent(appContext)
+            .child(new BannerMessageWidget())
             .child(new FlexContainer("column")
                 .id("launcher-pane")
                 .css("width", "53px")
diff --git a/src/public/app/services/timer.js b/src/public/app/services/timer.js
new file mode 100644
index 0000000000..d966b0a985
--- /dev/null
+++ b/src/public/app/services/timer.js
@@ -0,0 +1,29 @@
+// https://stackoverflow.com/a/3969760
+export default class Timer {
+    timerId;
+    start;
+    remaining;
+    callback;
+
+    constructor(callback, delay) {
+        this.remaining = delay;
+        this.callback = callback;
+
+        this.resume()
+    }
+
+    pause() {
+        clearTimeout(this.timerId);
+        this.remaining -= Date.now() - this.start;
+    }
+
+    resume() {
+        this.start = Date.now();
+        clearTimeout(this.timerId);
+        this.timerId = setTimeout(this.callback, this.remaining);
+    }
+
+    clear() {
+        clearTimeout(this.timerId);
+    }
+}
diff --git a/src/public/app/widgets/banner_message.js b/src/public/app/widgets/banner_message.js
new file mode 100644
index 0000000000..d7679e2b77
--- /dev/null
+++ b/src/public/app/widgets/banner_message.js
@@ -0,0 +1,158 @@
+import BasicWidget from "./basic_widget.js";
+import Timer from "../services/timer.js";
+
+const TLP = `
+    <div id="banner-message" class="empty">
+        <style>       
+            @keyframes bannerMessageTimer {
+                0% {
+                    transform: scaleX(1);  
+                }
+                100% {
+                    transform: scaleX(0);
+                }
+            }
+            
+            @keyframes bannerMessageTimerIndefinite {
+                0%, 100% {
+                    opacity: 0.4;
+                }
+                40% {
+                    opacity: 0;
+                }
+            }
+         
+            #banner-message {
+                text-align: center;
+                font-weight: 900;
+                font-size: 1rem;
+                width: 100%;
+                color: var(--banner-color);
+                background: var(--banner-background-color);
+                
+                position: absolute;
+                top: 0;
+                left: 0;
+                z-index: 6;
+            }
+            
+            #banner-message > p {
+                margin: 0;
+                padding: 5px 20px;
+            }
+            
+            #banner-message.empty > p {
+                padding: 0;
+            }
+            
+            #banner-message > .timer {
+                position: absolute;
+                left: 0;
+                bottom: 0;
+                width: 100%;
+                height: 1px;
+                background: #fff;
+                opacity: .4;
+                animation: bannerMessageTimer linear 5s forwards;
+                transform-origin: left;
+                will-change: transform;
+            }
+            
+            #banner-message > .timer.indefinite {
+                animation: bannerMessageTimerIndefinite linear 1s infinite;
+            }
+        </style>
+        <p></p>
+        <div class="timer"></div>
+    </div>
+`;
+
+const AVAILABLE_TYPES = new Set([
+    "error", "info", "warning", "success", "plain"
+]);
+
+export default class BannerMessageWidget extends BasicWidget {
+    durationTimer;
+
+    constructor() {
+        super();
+    }
+
+    doRender() {
+        this.$widget = $(TLP);
+        this.$bannerParagraph = this.$widget.find("p");
+        this.$timer = this.$widget.find(".timer");
+
+        this.$widget.on("mouseenter", this.pauseTimer.bind(this));
+        this.$widget.on("mouseleave", this.resumeTimer.bind(this));
+    }
+
+    hideBanner() {
+        this.$bannerParagraph.text("");
+        this.$widget.removeClass();
+        this.$widget.addClass("empty");
+
+        // In case `hideBanner` is called before the actual end, clear timer to avoid hard bugs
+        this.durationTimer?.clear();
+        this.durationTimer = undefined;
+    }
+
+    pauseTimer() {
+        if (this.durationTimer) {
+            this.$timer.css({
+                animationPlayState: "paused",
+            });
+            this.durationTimer?.pause();
+        }
+    }
+
+    resumeTimer() {
+        if (this.durationTimer) {
+            this.$timer.css({
+                animationPlayState: "",
+            });
+            this.durationTimer?.resume();
+        }
+    }
+
+    /**
+     * Shows a top banner.
+     * @param text - string: The text that should be displayed
+     * @param type - string: Type of the banner ("error", "info", "warning", "success", "plain")
+     * @param duration - number?: How long to show the banner. If `none` or `undefined`,
+     * the banner will not automatically be hidden.
+     */
+    setBannerEvent({
+        text,
+        type = "alert",
+        duration,
+    }) {
+        if (!text) {
+            this.hideBanner();
+            return;
+        }
+
+        const className = AVAILABLE_TYPES.has(type) ? type : "plain";
+
+        this.$bannerParagraph.text(text);
+        this.$widget.removeClass();
+        this.$widget.addClass(className);
+        this.$timer.removeClass("indefinite");
+
+        // Remove old timer to avoid hard bug
+        this.durationTimer?.clear();
+
+        if (duration) {
+            this.durationTimer = new Timer(this.hideBanner.bind(this), duration);
+            this.$timer.css({
+                animationDuration: `${duration}ms`
+            })
+        } else {
+            this.$timer.addClass("indefinite");
+        }
+    }
+
+    hideBannerEvent() {
+        this.hideBanner();
+    }
+}
diff --git a/src/public/app/widgets/buttons/calendar.js b/src/public/app/widgets/buttons/calendar.js
index 85d541c957..a592813cc8 100644
--- a/src/public/app/widgets/buttons/calendar.js
+++ b/src/public/app/widgets/buttons/calendar.js
@@ -30,6 +30,13 @@ const DROPDOWN_TPL = `
 export default class CalendarWidget extends RightDropdownButtonWidget {
     constructor() {
         super("bx-calendar", "Calendar", DROPDOWN_TPL);
+
+        setTimeout(() => {
+            this.triggerEvent("setBanner", {
+                text: "Internet lost.",
+                type: "error"
+            })
+        }, 200);
     }
 
     doRender() {
diff --git a/src/public/stylesheets/theme-dark.css b/src/public/stylesheets/theme-dark.css
index 3c6009b636..e70ec6e3d5 100644
--- a/src/public/stylesheets/theme-dark.css
+++ b/src/public/stylesheets/theme-dark.css
@@ -64,6 +64,9 @@
     --link-color: lightskyblue;
 
     --mermaid-theme: dark;
+
+    --banner-background-color: #DA321B;
+    --banner-color: var(--main-text-color);
 }
 
 body .global-menu-button {
diff --git a/src/public/stylesheets/theme-light.css b/src/public/stylesheets/theme-light.css
index 82fb21d9b4..ba4161b343 100644
--- a/src/public/stylesheets/theme-light.css
+++ b/src/public/stylesheets/theme-light.css
@@ -68,4 +68,7 @@ html {
     --link-color: blue;
 
     --mermaid-theme: default;
+
+    --banner-background-color: #DA321B;
+    --banner-color: var(--main-text-color);
 }