There's no need for all that box.
<input id="code1"
name="code"
type="text"
<input id="code1"
name="code"
type="text"
minlength="2"
maxlength="2"
pattern="[a-zA-Z0-9]*" />
minlength="2"
maxlength="2"
pattern="[a-zA-Z0-9]*" />
<input id="code2"
name="code"
type="text"
<input id="code2"
name="code"
type="text"
minlength="2"
maxlength="2"
pattern="[a-zA-Z0-9]*" />
minlength="2"
maxlength="2"
pattern="[a-zA-Z0-9]*" />
<input id="code3"
name="code"
type="text"
<input id="code3"
name="code"
type="text"
minlength="2"
maxlength="2"
pattern="[a-zA-Z0-9]*" />
minlength="2"
maxlength="2"
pattern="[a-zA-Z0-9]*" />