Start with default generated template

templates/misc/progress-bar.html.twig

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+{#
+/**
+ * @file
+ * Theme override for a progress bar.
+ *
+ * Note that the core Batch API uses this only for non-JavaScript batch jobs.
+ *
+ * Available variables:
+ * - label: The label of the working task.
+ * - percent: The percentage of the progress.
+ * - message: A string containing information to be displayed.
+ */
+#}
+{{ attach_library('aaron/progress') }}
+<div class="progress" data-drupal-progress>
+  {% if label %}
+    <div class="progress__label">{{ label }}</div>
+  {% endif %}
+  <div class="progress__track"><div class="progress__bar" style="width: {{ percent }}%"></div></div>
+  <div class="progress__percentage">{{ percent }}%</div>
+  <div class="progress__description">{{ message }}</div>
+</div>

templates/misc/status-messages.html.twig

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+{#
+/**
+ * @file
+ * Theme override for status messages.
+ *
+ * Displays status, error, and warning messages, grouped by type.
+ *
+ * An invisible heading identifies the messages for assistive technology.
+ * Sighted users see a colored box. See https://www.w3.org/TR/WCAG-TECHS/H69.html
+ * for info.
+ *
+ * Add an ARIA label to the contentinfo area so that assistive technology
+ * user agents will better describe this landmark.
+ *
+ * Available variables:
+ * - message_list: List of messages to be displayed, grouped by type.
+ * - status_headings: List of all status types.
+ * - attributes: HTML attributes for the element, including:
+ *   - class: HTML classes.
+ */
+#}
+<div data-drupal-messages>
+{% block messages %}
+{% for type, messages in message_list %}
+  {%
+    set classes = [
+      'messages',
+      'messages--' ~ type,
+    ]
+  %}
+  <div role="contentinfo" aria-label="{{ status_headings[type] }}"{{ attributes.addClass(classes)|without('role', 'aria-label') }}>
+    {% if type == 'error' %}
+      <div role="alert">
+    {% endif %}
+      {% if status_headings[type] %}
+        <h2 class="visually-hidden">{{ status_headings[type] }}</h2>
+      {% endif %}
+      {% if messages|length > 1 %}
+        <ul class="messages__list">
+          {% for message in messages %}
+            <li class="messages__item">{{ message }}</li>
+          {% endfor %}
+        </ul>
+      {% else %}
+        {{ messages|first }}
+      {% endif %}
+    {% if type == 'error' %}
+      </div>
+    {% endif %}
+  </div>
+  {# Remove type specific classes. #}
+  {% set attributes = attributes.removeClass(classes) %}
+{% endfor %}
+{% endblock messages %}
+</div>