How to remove the border highlight on an input text element

To remove it from all inputs

input {
 outline:none;
}

Before you do that, keep in mind that the focus outline is an accessibility and usability feature; it clues the user into what element is currently focused, and a lot of users depend on it. You need to find some other means to make focus visible.

In your case, try:

input.middle:focus {
    outline-width: 0;
}

Or in general, to affect all basic form elements:

input:focus,
select:focus,
textarea:focus,
button:focus {
    outline: none;
}

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In the comments, Noah Whitmore suggested taking this even further to support elements that have the contenteditable attribute set to true (effectively making them a type of input element). The following should target those as well (in CSS3 capable browsers):

[contenteditable="true"]:focus {
    outline: none;
}

Although I wouldn't recommend it, for completeness' sake, you could always disable the focus outline on everything with this:

*:focus {
    outline: none;
}