Hey Andrew,
This should help:
https://compojoom.com/blog/entry/how-to-use-firebug-to-change-the-css-of-a-joomla-extension

Regards,
Daniel

Hi,
Thank you, I have looked everywhere, in administrator, components, modules, etc. and made changes to most things that have a line height of 18px.
According to firebug I am looking for input#jform_cmc_groups_EMAIL.inputbox.input-medium.cmc_req.validate-email.required.invalid 150pxX18
I can find a few that refer to input width 150px but not with a height of 18px.
Sorry, can you help me find the specific file that needs changed?
Thanks, Andrew

Hey Andrew,
You don't make the change in the file where the code is written. If you do the change there, the next time you update you will lose it.
Normally most templates have a custom.css file - this is where you should place your css.
in this specific case notice that the height is set in boostrap-form.css on line 26:

.cmc-signup select, .cmc-signup textarea, .cmc-signup input[type="text"], .cmc-signup input[type="password"], .cmc-signup input[type="datetime"], .cmc-signup input[type="datetime-local"], .cmc-signup input[type="date"], .cmc-signup input[type="month"], .cmc-signup input[type="time"], .cmc-signup input[type="week"], .cmc-signup input[type="number"], .cmc-signup input[type="email"], .cmc-signup input[type="url"], .cmc-signup input[type="search"], .cmc-signup input[type="tel"], .cmc-signup input[type="color"], .cmc-signup .uneditable-input {

    border-radius: 3px;

    color: #555;

    display: inline-block;

    font-size: 13px;

    height: 18px;

    line-height: 18px;

    margin-bottom: 9px;

    padding: 4px 6px;

    vertical-align: middle;

}

in your custom.css file you have several options to change this. Either by using

.cmc-signup input {

    height: 20px !important;

}

Note the use of !important. We have to use this as the .cmc-signup input is not that specific as .cmc-signup input[type...]

Regards,
Daniel

Or you could directly style the element using it's id:
#jform_cmc_groups_EMAIL {
height: 20px;
}