Add placeholders and fix test

Author: kochaika

introduction/page_structure/visual attributes/index.html

@@ -1,5 +1,5 @@
-<h1> The heading will be blue because the color is set in the style attribute </h1>
+<h1 style="color: blue;"> The heading will be blue because the color is set in the style attribute </h1>
 
-<p> The attribute hides the element on a page; the element won't be displayed </p>
+<p hidden> The attribute hides the element on a page; the element won't be displayed </p>
 
-<button> The button with the attribute disabled will be blocked</button>
+<button disabled> The button with the attribute disabled will be blocked</button>

introduction/page_structure/visual attributes/task-info.yaml

@@ -1,12 +1,25 @@
 type: edu
 files:
-- name: task.py
-  visible: false
-- name: tests/test_task.py
-  visible: false
-- name: __init__.py
-  visible: false
-- name: tests/__init__.py
-  visible: false
-- name: index.html
-  visible: true
+  - name: index.html
+    visible: true
+    placeholders:
+      - offset: 3
+        length: 21
+        placeholder_text: ""
+        is_visible: false
+      - offset: 108
+        length: 7
+        placeholder_text: ""
+        is_visible: false
+      - offset: 204
+        length: 9
+        placeholder_text: ""
+        is_visible: false
+  - name: task.py
+    visible: false
+  - name: tests/test_task.py
+    visible: false
+  - name: __init__.py
+    visible: false
+  - name: tests/__init__.py
+    visible: false

introduction/page_structure/visual attributes/task.md

@@ -7,12 +7,13 @@ may be necessary for element locating in tests.
 
 Here are examples of attributes that affect rendering and the element's behavior: 
 
-```
+```html
 <h1 style="color: blue;"> The heading will be blue because the color is set in the style attribute </h1>
 
 <p hidden> The attribute hidden hides the element on a page; the element won't be displayed </p>
 
 <button disabled> The button with the attribute disabled will be blocked </button>
 ```
 
+### Task
 Try opening `index.html` in your browser. Now add the visual attributes and try opening this file again. 

introduction/page_structure/visual attributes/tests/test_task.py

@@ -13,7 +13,7 @@ def test_add(self):
         try:
             self.assertTrue(soup.h1["style"] == "color: blue;", f"Should be color: blue style, got {soup.h1['style']}")
             self.assertTrue("hidden" in str(soup.p), f"Should be hidden paragraph")
-            self.assertTrue("disabled" in str(soup.button), f"Should be disabled button")
+            self.assertTrue("disabled" in str(soup.button).split('>')[0], f"Should be disabled button")
 
         except Exception as e:
             self.fail("wrong page structure")