Fix heading levels

[estelle]

Don't start the heading sequence with H3

[github-actions]

Preview URLs (6 pages)

• /en-US/docs/Web/CSS/CSS_animations
• /en-US/docs/Web/CSS/CSS_basic_user_interface
• /en-US/docs/Web/CSS/CSS_colors
• /en-US/docs/Web/CSS/CSS_compositing_and_blending
• /en-US/docs/Web/CSS/CSS_filter_effects
• /en-US/docs/Web/CSS/CSS_generated_content

Flaws (4)

Note! 2 documents with no flaws that don't need to be listed. 🎉

URL: /en-US/docs/Web/CSS/CSS_animations
Title: CSS animations
Flaw count: 1

• macros:
  • Macro produces link /en-US/docs/Learn_web_development/Core/Styling_basics/Cool-looking_box which is a redirect

---

URL: /en-US/docs/Web/CSS/CSS_compositing_and_blending
Title: CSS compositing and blending
Flaw count: 1

• macros:
  • Macro produces link /en-US/docs/Learn_web_development/Core/Styling_basics/Cool-looking_box which is a redirect

---

URL: /en-US/docs/Web/CSS/CSS_filter_effects
Title: CSS filter effects
Flaw count: 1

• macros:
  • Macro produces link /en-US/docs/Learn_web_development/Core/Styling_basics/Cool-looking_box which is a redirect

---

URL: /en-US/docs/Web/CSS/CSS_generated_content
Title: CSS generated content
Flaw count: 1

• macros:
  • Macro produces link /en-US/docs/Learn_web_development/Core/Styling_basics/Cool-looking_box which is a redirect

[chrisdavidmills]

LGTM!