feat: implement milestone-based progress system and activate new lessons

Progress System:
- Replace percentage-based progress with milestone markers (1, 5, 10, 20, 30, 50, 75, 100)
- Add visual milestone indicators with reached/current/next states
- Add celebration animation when milestones are reached
- Update progress bar to show progress toward next milestone
- Add progressTextMilestone i18n key for all 6 languages

New Lessons Activated:
- HTML Dialog (native modal dialogs)
- HTML Progress & Meter (indicator elements)
- HTML Fieldset (form grouping)
- HTML Datalist (autocomplete inputs)

This adds 10 new lessons across all 6 languages, bringing total from ~66 to ~76.

src/app.js

@@ -165,6 +165,7 @@ const elements = {
 	sectionFooterLessonLinks: document.getElementById("section-footer-lesson-links"),
 	progressFill: document.getElementById("progress-fill"),
 	progressText: document.getElementById("progress-text"),
+	milestonesContainer: document.getElementById("milestones"),
 	resetBtn: document.getElementById("reset-btn"),
 	disableFeedbackToggle: document.getElementById("disable-feedback-toggle"),
 
@@ -310,14 +311,48 @@ function showSuccessHint(message) {
 
 // ================= PROGRESS DISPLAY =================
 
+// Track last milestone to detect new achievements
+let lastMilestoneReached = 0;
+
 function updateProgressDisplay() {
 	const stats = lessonEngine.getProgressStats();
-	elements.progressFill.style.width = `${stats.percentComplete}%`;
+
-	elements.progressText.textContent = t("progressText", {
+	// Update progress bar (now shows progress to next milestone)
-		percent: stats.percentComplete,
+	elements.progressFill.style.width = `${stats.progressToNext}%`;
+
+	// Update progress text
+	elements.progressText.textContent = t("progressTextMilestone", {
 		completed: stats.totalCompleted,
-		total: stats.totalLessons
+		next: stats.nextMilestone
 	});
+
+	// Update milestone indicators
+	if (elements.milestonesContainer) {
+		const milestoneEls = elements.milestonesContainer.querySelectorAll(".milestone");
+		milestoneEls.forEach((el) => {
+			const value = parseInt(el.dataset.value, 10);
+			el.classList.remove("reached", "current", "next", "just-reached");
+
+			if (stats.milestonesReached.includes(value)) {
+				el.classList.add("reached");
+				// Check if this milestone was just reached
+				if (value > lastMilestoneReached && value === stats.currentMilestone) {
+					el.classList.add("just-reached");
+				}
+			} else if (value === stats.nextMilestone) {
+				el.classList.add("next");
+			}
+
+			if (value === stats.currentMilestone) {
+				el.classList.add("current");
+			}
+		});
+	}
+
+	// Update last milestone for celebration detection
+	if (stats.currentMilestone > lastMilestoneReached) {
+		lastMilestoneReached = stats.currentMilestone;
+	}
 }
 
 // ================= USER SETTINGS =================

src/auth.js

@@ -261,12 +261,18 @@ function setupAuthForms() {
     });
 
   // OAuth buttons
-  document.getElementById("google-login")?.addEventListener("click", () => {
+  document.getElementById("google-login")?.addEventListener("click", async () => {
-    authModule?.signInWithGoogle();
+    const { error } = await authModule?.signInWithGoogle() ?? { error: null };
+    if (error) {
+      showOAuthError(error.message);
+    }
   });
 
-  document.getElementById("github-login")?.addEventListener("click", () => {
+  document.getElementById("github-login")?.addEventListener("click", async () => {
-    authModule?.signInWithGitHub();
+    const { error } = await authModule?.signInWithGitHub() ?? { error: null };
+    if (error) {
+      showOAuthError(error.message);
+    }
   });
 
   // Close dialog on backdrop click
@@ -364,6 +370,22 @@ async function handleResetSubmit(e) {
   }
 }
 
+function showOAuthError(message) {
+  // Show error in the currently visible form's error element
+  const loginError = document.getElementById("login-error");
+  const signupError = document.getElementById("signup-error");
+
+  // Use whichever form is visible
+  const errorEl = !document.getElementById("login-form")?.classList.contains("hidden")
+    ? loginError
+    : signupError;
+
+  if (errorEl) {
+    errorEl.textContent = message;
+    errorEl.classList.remove("hidden");
+  }
+}
+
 function switchForm(formName) {
   const loginForm = document.getElementById("login-form");
   const signupForm = document.getElementById("signup-form");

src/config/lessons.js

@@ -16,6 +16,10 @@ import htmlElementsEN from "../../lessons/20-html-elements.json";
 import htmlFormsBasicEN from "../../lessons/21-html-forms-basic.json";
 import htmlFormsValidationEN from "../../lessons/22-html-forms-validation.json";
 import htmlDetailsSummaryEN from "../../lessons/23-html-details-summary.json";
+import htmlProgressMeterEN from "../../lessons/24-html-progress-meter.json";
+import htmlDatalistEN from "../../lessons/25-html-datalist.json";
+import htmlDialogEN from "../../lessons/27-html-dialog.json";
+import htmlFieldsetEN from "../../lessons/28-html-forms-fieldset.json";
 import htmlFigureEN from "../../lessons/29-html-figure.json";
 import htmlTablesEN from "../../lessons/30-html-tables.json";
 import htmlSvgEN from "../../lessons/32-html-svg.json";
@@ -35,6 +39,10 @@ import htmlElementsDE from "../../lessons/de/20-html-elements.json";
 import htmlFormsBasicDE from "../../lessons/de/21-html-forms-basic.json";
 import htmlFormsValidationDE from "../../lessons/de/22-html-forms-validation.json";
 import htmlDetailsSummaryDE from "../../lessons/de/23-html-details-summary.json";
+import htmlProgressMeterDE from "../../lessons/de/24-html-progress-meter.json";
+import htmlDatalistDE from "../../lessons/de/25-html-datalist.json";
+import htmlDialogDE from "../../lessons/de/27-html-dialog.json";
+import htmlFieldsetDE from "../../lessons/de/28-html-forms-fieldset.json";
 import htmlTablesDE from "../../lessons/de/30-html-tables.json";
 import htmlSvgDE from "../../lessons/de/32-html-svg.json";
 import flexboxDE from "../../lessons/de/flexbox.json";
@@ -50,6 +58,10 @@ import htmlElementsPL from "../../lessons/pl/20-html-elements.json";
 import htmlFormsBasicPL from "../../lessons/pl/21-html-forms-basic.json";
 import htmlFormsValidationPL from "../../lessons/pl/22-html-forms-validation.json";
 import htmlDetailsSummaryPL from "../../lessons/pl/23-html-details-summary.json";
+import htmlProgressMeterPL from "../../lessons/pl/24-html-progress-meter.json";
+import htmlDatalistPL from "../../lessons/pl/25-html-datalist.json";
+import htmlDialogPL from "../../lessons/pl/27-html-dialog.json";
+import htmlFieldsetPL from "../../lessons/pl/28-html-forms-fieldset.json";
 import htmlTablesPL from "../../lessons/pl/30-html-tables.json";
 import htmlSvgPL from "../../lessons/pl/32-html-svg.json";
 import flexboxPL from "../../lessons/pl/flexbox.json";
@@ -65,6 +77,10 @@ import htmlElementsES from "../../lessons/es/20-html-elements.json";
 import htmlFormsBasicES from "../../lessons/es/21-html-forms-basic.json";
 import htmlFormsValidationES from "../../lessons/es/22-html-forms-validation.json";
 import htmlDetailsSummaryES from "../../lessons/es/23-html-details-summary.json";
+import htmlProgressMeterES from "../../lessons/es/24-html-progress-meter.json";
+import htmlDatalistES from "../../lessons/es/25-html-datalist.json";
+import htmlDialogES from "../../lessons/es/27-html-dialog.json";
+import htmlFieldsetES from "../../lessons/es/28-html-forms-fieldset.json";
 import htmlTablesES from "../../lessons/es/30-html-tables.json";
 import htmlSvgES from "../../lessons/es/32-html-svg.json";
 import flexboxES from "../../lessons/es/flexbox.json";
@@ -80,6 +96,10 @@ import htmlElementsAR from "../../lessons/ar/20-html-elements.json";
 import htmlFormsBasicAR from "../../lessons/ar/21-html-forms-basic.json";
 import htmlFormsValidationAR from "../../lessons/ar/22-html-forms-validation.json";
 import htmlDetailsSummaryAR from "../../lessons/ar/23-html-details-summary.json";
+import htmlProgressMeterAR from "../../lessons/ar/24-html-progress-meter.json";
+import htmlDatalistAR from "../../lessons/ar/25-html-datalist.json";
+import htmlDialogAR from "../../lessons/ar/27-html-dialog.json";
+import htmlFieldsetAR from "../../lessons/ar/28-html-forms-fieldset.json";
 import htmlTablesAR from "../../lessons/ar/30-html-tables.json";
 import htmlSvgAR from "../../lessons/ar/32-html-svg.json";
 import flexboxAR from "../../lessons/ar/flexbox.json";
@@ -95,6 +115,10 @@ import htmlElementsUK from "../../lessons/uk/20-html-elements.json";
 import htmlFormsBasicUK from "../../lessons/uk/21-html-forms-basic.json";
 import htmlFormsValidationUK from "../../lessons/uk/22-html-forms-validation.json";
 import htmlDetailsSummaryUK from "../../lessons/uk/23-html-details-summary.json";
+import htmlProgressMeterUK from "../../lessons/uk/24-html-progress-meter.json";
+import htmlDatalistUK from "../../lessons/uk/25-html-datalist.json";
+import htmlDialogUK from "../../lessons/uk/27-html-dialog.json";
+import htmlFieldsetUK from "../../lessons/uk/28-html-forms-fieldset.json";
 import htmlTablesUK from "../../lessons/uk/30-html-tables.json";
 import htmlSvgUK from "../../lessons/uk/32-html-svg.json";
 import flexboxUK from "../../lessons/uk/flexbox.json";
@@ -121,8 +145,12 @@ const moduleStoreEN = [
 	htmlSvgEN,
 	// HTML Interactive
 	htmlDetailsSummaryEN,
+	htmlDialogEN,
+	htmlProgressMeterEN,
 	htmlFormsBasicEN,
 	htmlFormsValidationEN,
+	htmlFieldsetEN,
+	htmlDatalistEN,
 	htmlTablesEN,
 	// Outro
 	goodbyeEN,
@@ -151,8 +179,12 @@ const moduleStoreDE = [
 	htmlSvgDE,
 	// HTML Interactive
 	htmlDetailsSummaryDE,
+	htmlDialogDE,
+	htmlProgressMeterDE,
 	htmlFormsBasicDE,
 	htmlFormsValidationDE,
+	htmlFieldsetDE,
+	htmlDatalistDE,
 	htmlTablesDE,
 	// Outro
 	goodbyeEN,
@@ -181,8 +213,12 @@ const moduleStorePL = [
 	htmlSvgPL,
 	// HTML Interactive
 	htmlDetailsSummaryPL,
+	htmlDialogPL,
+	htmlProgressMeterPL,
 	htmlFormsBasicPL,
 	htmlFormsValidationPL,
+	htmlFieldsetPL,
+	htmlDatalistPL,
 	htmlTablesPL,
 	// Outro
 	goodbyeEN,
@@ -211,8 +247,12 @@ const moduleStoreES = [
 	htmlSvgES,
 	// HTML Interactive
 	htmlDetailsSummaryES,
+	htmlDialogES,
+	htmlProgressMeterES,
 	htmlFormsBasicES,
 	htmlFormsValidationES,
+	htmlFieldsetES,
+	htmlDatalistES,
 	htmlTablesES,
 	// Outro
 	goodbyeEN,
@@ -241,8 +281,12 @@ const moduleStoreAR = [
 	htmlSvgAR,
 	// HTML Interactive
 	htmlDetailsSummaryAR,
+	htmlDialogAR,
+	htmlProgressMeterAR,
 	htmlFormsBasicAR,
 	htmlFormsValidationAR,
+	htmlFieldsetAR,
+	htmlDatalistAR,
 	htmlTablesAR,
 	// Outro
 	goodbyeEN,
@@ -271,8 +315,12 @@ const moduleStoreUK = [
 	htmlSvgUK,
 	// HTML Interactive
 	htmlDetailsSummaryUK,
+	htmlDialogUK,
+	htmlProgressMeterUK,
 	htmlFormsBasicUK,
 	htmlFormsValidationUK,
+	htmlFieldsetUK,
+	htmlDatalistUK,
 	htmlTablesUK,
 	// Outro
 	goodbyeEN,

src/i18n.js

@@ -39,6 +39,7 @@ const translations = {
 		language: "Language",
 		progress: "Progress",
 		progressText: "{percent}% Complete ({completed}/{total})",
+		progressTextMilestone: "{completed} of {next}",
 		lessons: "Lessons",
 		settings: "Settings",
 		showHints: "Show Hints",
@@ -260,6 +261,7 @@ const translations = {
 		language: "Sprache",
 		progress: "Fortschritt",
 		progressText: "{percent}% abgeschlossen ({completed}/{total})",
+		progressTextMilestone: "{completed} von {next}",
 		lessons: "Lektionen",
 		settings: "Einstellungen",
 		showHints: "Hinweise anzeigen",
@@ -481,6 +483,7 @@ const translations = {
 		language: "Język",
 		progress: "Postęp",
 		progressText: "{percent}% ukończone ({completed}/{total})",
+		progressTextMilestone: "{completed} z {next}",
 		lessons: "Lekcje",
 		settings: "Ustawienia",
 		showHints: "Pokaż podpowiedzi",
@@ -701,6 +704,7 @@ const translations = {
 		language: "Idioma",
 		progress: "Progreso",
 		progressText: "{percent}% completado ({completed}/{total})",
+		progressTextMilestone: "{completed} de {next}",
 		lessons: "Lecciones",
 		settings: "Configuración",
 		showHints: "Mostrar pistas",
@@ -923,6 +927,7 @@ const translations = {
 		language: "اللغة",
 		progress: "التقدم",
 		progressText: "{percent}% مكتمل ({completed}/{total})",
+		progressTextMilestone: "{completed} من {next}",
 		lessons: "الدروس",
 		settings: "الإعدادات",
 		showHints: "إظهار التلميحات",
@@ -1140,6 +1145,7 @@ const translations = {
 		language: "Мова",
 		progress: "Прогрес",
 		progressText: "{percent}% завершено ({completed}/{total})",
+		progressTextMilestone: "{completed} з {next}",
 		lessons: "Уроки",
 		settings: "Налаштування",
 		showHints: "Показувати підказки",

src/impl/LessonEngine.js

@@ -472,10 +472,11 @@ export class LessonEngine {
 	}
 
 	/**
-	 * Get overall progress statistics
+	 * Get overall progress statistics with milestone data
-	 * @returns {Object} Progress statistics
+	 * @returns {Object} Progress statistics including milestone progress
 	 */
 	getProgressStats() {
+		const MILESTONES = [1, 5, 10, 20, 30, 50, 75, 100];
 		let totalLessons = 0;
 		let totalCompleted = 0;
 
@@ -490,10 +491,25 @@ export class LessonEngine {
 			}
 		});
 
+		// Calculate milestone progress
+		const milestonesReached = MILESTONES.filter((m) => totalCompleted >= m);
+		const currentMilestone = milestonesReached[milestonesReached.length - 1] || 0;
+		const nextMilestone = MILESTONES.find((m) => m > totalCompleted) || 100;
+		const progressToNext =
+			nextMilestone > currentMilestone
+				? Math.round(((totalCompleted - currentMilestone) / (nextMilestone - currentMilestone)) * 100)
+				: 100;
+
 		return {
 			totalLessons,
 			totalCompleted,
-			percentComplete: totalLessons > 0 ? Math.round((totalCompleted / totalLessons) * 100) : 0
+			percentComplete: totalLessons > 0 ? Math.round((totalCompleted / totalLessons) * 100) : 0,
+			// Milestone data
+			milestones: MILESTONES,
+			milestonesReached,
+			currentMilestone,
+			nextMilestone,
+			progressToNext
 		};
 	}
 

src/index.html

@@ -468,11 +468,21 @@
 
 				<div class="sidebar-section">
 					<h4 data-i18n="progress">Progress</h4>
-					<div class="progress-display" id="progress-display">
+					<div class="progress-display milestone-progress" id="progress-display">
+						<div class="milestones" id="milestones">
+							<span class="milestone" data-value="1">1</span>
+							<span class="milestone" data-value="5">5</span>
+							<span class="milestone" data-value="10">10</span>
+							<span class="milestone" data-value="20">20</span>
+							<span class="milestone" data-value="30">30</span>
+							<span class="milestone" data-value="50">50</span>
+							<span class="milestone" data-value="75">75</span>
+							<span class="milestone" data-value="100">100</span>
+						</div>
 						<div class="progress-bar">
 							<div class="progress-fill" id="progress-fill"></div>
 						</div>
-						<span class="progress-text" id="progress-text">0% Complete</span>
+						<span class="progress-text" id="progress-text">0 of 100</span>
 					</div>
 				</div>
 

src/main.css

@@ -1019,6 +1019,65 @@ nav.sidebar-section {
 	color: var(--light-text);
 }
 
+/* Milestone Progress */
+.milestone-progress {
+	gap: var(--spacing-sm);
+}
+
+.milestones {
+	display: flex;
+	justify-content: space-between;
+	padding: 0 2px;
+}
+
+.milestone {
+	display: flex;
+	align-items: center;
+	justify-content: center;
+	min-width: 24px;
+	height: 24px;
+	font-size: 0.7rem;
+	font-weight: 600;
+	color: var(--light-text);
+	background: var(--border-color);
+	border-radius: 50%;
+	transition: all 0.3s ease;
+}
+
+.milestone.reached {
+	background: linear-gradient(135deg, #9163b8, #7c4dff);
+	color: white;
+}
+
+.milestone.current {
+	background: linear-gradient(135deg, #d45aa0, #1aafb8);
+	color: white;
+	transform: scale(1.15);
+	box-shadow: 0 2px 8px rgba(212, 90, 160, 0.4);
+}
+
+.milestone.next {
+	border: 2px dashed var(--light-text);
+	background: transparent;
+}
+
+/* Milestone celebration animation */
+@keyframes milestone-pop {
+	0% {
+		transform: scale(1);
+	}
+	50% {
+		transform: scale(1.4);
+	}
+	100% {
+		transform: scale(1.15);
+	}
+}
+
+.milestone.just-reached {
+	animation: milestone-pop 0.5s ease-out;
+}
+
 /* Module List in Sidebar */
 .module-list {
 	/* No max-height - parent nav.sidebar-section handles overflow */