I'm using html error messages
<form>
<input required />
<input type="submit" />
</form>
My question is: can the sign be modified? make it bigger, change the color and other ... I show it in an image
Before there was a way to do it in chrome with the pseudo-elements, but they stopped working in 2013.
::-webkit-validation-bubble
::-webkit-validation-bubble-arrow-clipper
::-webkit-validation-bubble-arrow
::-webkit-validation-bubble-message
The only way to implement your custom style is to make a validation system from scratch.
It is not possible to change message styles for validation errors since these are browser-specific. Before it could be done in chrome
form_validation_messages using pseudo-elementos
::-webkit-validation-bubble
::-webkit-validation-bubble-arrow
::-webkit-validation-bubble-arrow-clipper
::-webkit-validation-bubble-heading
::-webkit-validation-bubble-message
::-webkit-validation-bubble-text-block
But as of versión 28
Chrome removed Support for these pseudo-elementos .
What you can do is change the message that appears:
<input required oninvalid="this.setCustomValidity('nuevo mensaje a mostrar')"/>