diff --git a/app/views/shared/issuable/_sidebar.html.haml b/app/views/shared/issuable/_sidebar.html.haml
index f166fac105dc08903ed11630783a1d24767ffc4b..0242765021968802eb92f9ef6ad5c5ee98e5ee4b 100644
--- a/app/views/shared/issuable/_sidebar.html.haml
+++ b/app/views/shared/issuable/_sidebar.html.haml
@@ -9,12 +9,12 @@
       %a.gutter-toggle.pull-right.js-sidebar-toggle{ role: "button", href: "#", aria: { label: "Toggle sidebar" } }
         = sidebar_gutter_toggle_icon
       - if current_user
-        %button.btn.btn-default.issuable-header-btn.pull-right.js-issuable-todo{ type: "button", aria: { label: (todo.nil? ? "Add Todo" : "Mark Done") }, data: { todo_text: "Add Todo", mark_text: "Mark Done", issuable_id: issuable.id, issuable_type: issuable.class.name.underscore, url: namespace_project_todos_path(@project.namespace, @project), delete_path: (dashboard_todo_path(todo) if todo) } }
+        %button.btn.btn-default.issuable-header-btn.pull-right.js-issuable-todo{ type: "button", aria: { label: (todo.nil? ? "Add todo" : "Mark done") }, data: { todo_text: "Add todo", mark_text: "Mark done", issuable_id: issuable.id, issuable_type: issuable.class.name.underscore, url: namespace_project_todos_path(@project.namespace, @project), delete_path: (dashboard_todo_path(todo) if todo) } }
           %span.js-issuable-todo-text
             - if todo
-              Mark Done
+              Mark done
             - else
-              Add Todo
+              Add todo
           = icon('spin spinner', class: 'hidden js-issuable-todo-loading')
 
     = form_for [@project.namespace.becomes(Namespace), @project, issuable], remote: true, format: :json, html: {class: 'issuable-context-form inline-update js-issuable-update'} do |f|
diff --git a/changelogs/unreleased/issue_24748.yml b/changelogs/unreleased/issue_24748.yml
new file mode 100644
index 0000000000000000000000000000000000000000..4c1df542c539a67869d2921e42811457181471c2
--- /dev/null
+++ b/changelogs/unreleased/issue_24748.yml
@@ -0,0 +1,4 @@
+---
+title: Fix title case to sentence case
+merge_request: 
+author: Luis Alonso Chavez Armendariz
diff --git a/doc/workflow/img/todos_add_todo_sidebar.png b/doc/workflow/img/todos_add_todo_sidebar.png
index 59175ae44c5c9fe535acb8c6678e44891e3ae862..3fa37067d1ecbe740a9a298a59526d0c7af4af0a 100644
Binary files a/doc/workflow/img/todos_add_todo_sidebar.png and b/doc/workflow/img/todos_add_todo_sidebar.png differ
diff --git a/doc/workflow/img/todos_mark_done_sidebar.png b/doc/workflow/img/todos_mark_done_sidebar.png
index aa35bb672ea97ea1028582741f717d8fbcd20b2f..a8e756a71db4211f1aa3434245e141f50af7fff6 100644
Binary files a/doc/workflow/img/todos_mark_done_sidebar.png and b/doc/workflow/img/todos_mark_done_sidebar.png differ
diff --git a/doc/workflow/todos.md b/doc/workflow/todos.md
index 54e7ae19ea524df1b240e55859da97c1a45a43b4..1a8fc39bb335288ebf77147cba28d51c5b6ea02a 100644
--- a/doc/workflow/todos.md
+++ b/doc/workflow/todos.md
@@ -35,7 +35,7 @@ A Todo appears in your Todos dashboard when:
 ### Manually creating a Todo
 
 You can also add an issue or merge request to your Todos dashboard by clicking
-the "Add Todo" button in the issue or merge request sidebar.
+the "Add todo" button in the issue or merge request sidebar.
 
 ![Adding a Todo from the issuable sidebar](img/todos_add_todo_sidebar.png)
 
@@ -69,7 +69,7 @@ corresponding **Done** button, and it will disappear from your Todo list.
 ![A Todo in the Todos dashboard](img/todo_list_item.png)
 
 A Todo can also be marked as done from the issue or merge request sidebar using
-the "Mark Done" button.
+the "Mark done" button.
 
 ![Mark Done from the issuable sidebar](img/todos_mark_done_sidebar.png)
 
diff --git a/spec/features/issues/todo_spec.rb b/spec/features/issues/todo_spec.rb
index de8fdda388dc7a109cd6e5c6eebcceec0c472934..41ff31d2b99b95fc7f5fa0c2a60a4b6e4a799c1c 100644
--- a/spec/features/issues/todo_spec.rb
+++ b/spec/features/issues/todo_spec.rb
@@ -13,8 +13,8 @@ feature 'Manually create a todo item from issue', feature: true, js: true do
 
   it 'creates todo when clicking button' do
     page.within '.issuable-sidebar' do
-      click_button 'Add Todo'
-      expect(page).to have_content 'Mark Done'
+      click_button 'Add todo'
+      expect(page).to have_content 'Mark done'
     end
 
     page.within '.header-content .todos-pending-count' do
@@ -30,8 +30,8 @@ feature 'Manually create a todo item from issue', feature: true, js: true do
 
   it 'marks a todo as done' do
     page.within '.issuable-sidebar' do
-      click_button 'Add Todo'
-      click_button 'Mark Done'
+      click_button 'Add todo'
+      click_button 'Mark done'
     end
 
     expect(page).to have_selector('.todos-pending-count', visible: false)
diff --git a/spec/javascripts/fixtures/right_sidebar.html.haml b/spec/javascripts/fixtures/right_sidebar.html.haml
index d48b77cf0ce2d4ba764fd2dd05e8e6e6557460e7..d259b58f235c7aedcfc9fb3bda3520dc34dca1e7 100644
--- a/spec/javascripts/fixtures/right_sidebar.html.haml
+++ b/spec/javascripts/fixtures/right_sidebar.html.haml
@@ -5,9 +5,9 @@
     %div.block.issuable-sidebar-header
       %a.gutter-toggle.pull-right.js-sidebar-toggle
         %i.fa.fa-angle-double-left
-      %button.btn.btn-default.issuable-header-btn.pull-right.js-issuable-todo{ type: "button", data: { todo_text: "Add Todo", mark_text: "Mark Done", issuable_id: "1", issuable_type: "issue", url: "/todos" }}
+      %button.btn.btn-default.issuable-header-btn.pull-right.js-issuable-todo{ type: "button", data: { todo_text: "Add todo", mark_text: "Mark done", issuable_id: "1", issuable_type: "issue", url: "/todos" }}
         %span.js-issuable-todo-text
-          Add Todo
+          Add todo
         %i.fa.fa-spin.fa-spinner.js-issuable-todo-loading.hidden
 
     %form.issuable-context-form