Don't use Text Box and other Form Control objects in your games, unless you absolutely need to. They are DOM elements, and have lots of issues - it's hard to style them, they are displayed above all layers, they have problems with positioning, they may be displayed differently in different browsers, they may "steal" focus and keyboard events will not work etc.
In your case I suggest using a simple text, or a sprite font, or maybe even a static sprite with a few frames if you don't have many tooltips in your game.
If you want your text to remain readable when shown on different backgrounds - use Sprite Font with an outline or its own background. Here is a very useful tool: