How can I advance style my form especially the buttons?

I really like the flat look shown in the demo of the Form Tabs widget, and the long, flat style of the next/back buttons in the Line Radio Button demo. How did you get that look? I added the Form Tabs, but it doesn't look the same. I tried the Line Radio Button, but it didn't seem to work. I also tried making the Next/Back buttons wider in the Advanced Designer, but the app wouldn't let me change the width. Is all this because I started with a theme, and don't know how to use CSS?

It's the Amber Orange theme of the Form Tabs widget. You can select that in the settings:

As for the next/back buttons, inject the following custom CSS codes in your form:

.form-all .form-pagebreak-back, .form-all .form-pagebreak-next {

    color: #ffffff !important;

    background: #f4ad04 !important;

    box-shadow: none !important;

    text-shadow: none;

    border: none !important;

}

Please follow the steps here to inject the codes: https://www.jotform.com/help/117-How-to-Inject-Custom-CSS-Codes. 

As for the line radio button, you mean the demo form, right? That is still in the widget settings. It is the Blue Color scheme. 

I followed the instructions and changed the theme in the Form Tabs
settings, and injected the code given. The tabs look good, but the Next
button still isn't what I was looking for. I've attached screen shots of
the demo whose look I was trying to achieve, and my form.
Thank you,
Rebecca Pitts
1SimplePhone
DFW 469-320-1111
MO 660-299-1111
MA 774-307-1111
IVR Recording Line 469-998-9144
3620 N Josey Ln, Ste 110
Carrollton, TX 75007
For immediate technical support
Please e-mail support@1simplephone.com
...

We did not receive you screenshot please attach them as guided in this article so we can see what you are trying to achieve. How-to-Post-Screenshots-to-Our-Support-Forum

If you have the sample, we should be able to suggest the custom CSS code for the Next button.

You can clone the demo form and edit the fields by following this guide: https://www.jotform.com/help/42-How-to-Clone-an-Existing-Form-from-a-URL

Also, I noticed on the screenshot you provided, I can see that the other image is a Card Form. Unfortunately, you cannot add custom CSS code to Card Form.

I hope this information helps.