Why DOM order defines keyboard navigation
Native interactive elements are a good starting point for understanding focus behavior because the browser inserts them into the tab order automatically, based on their position in the DOM. Three buttons placed one after another, for example, will receive focus in that same sequence as the user presses Tab.
<button>I Should</button>
<button>Be Focused</button>
<button>Last!</button>
Trouble appears when CSS changes the visual arrangement without touching the DOM. A float can move a button to the right side of the screen, yet the underlying DOM order—and therefore the tab order—stays unchanged. Users tabbing through the page then hit elements in a sequence that no longer matches what they see. The Web AIM checklist addresses this in section 1.3.2: the reading and navigation order, as determined by code order, should be logical and intuitive.
<button style="float: right">I Should</button>
<button>Be Focused</button>
<button>Last!</button>
It is easy to introduce this kind of mismatch without noticing. A practical habit is to tab through pages regularly, specifically to confirm that focus follows a sensible, visible path.
Handling offscreen content that steals focus
Offscreen elements present a related problem. Content such as a responsive side-nav may need to remain in the DOM even when hidden. If those elements can still receive focus, the user's cursor seems to disappear and then reappear somewhere unexpected while tabbing—clearly undesirable. The goal is to prevent the panel from gaining focus until it is actually visible and interactive.
When focus seems to vanish, the console can help you locate it. Checking document.activeElement reveals which element currently holds focus, letting you identify the hidden culprit.
Once the problem element is known, the fix is to hide it properly with display: none or visibility: hidden, and then restore it to display: block or visibility: visible before presenting it to the user.
Before publishing, tab through your site to verify that focus does not jump out of sequence or disappear altogether. If it does, either hide offscreen content with display: none or visibility: hidden, or move the affected elements to a logical position in the DOM.
