Custom CSS applies in design mode but not when the form is previewed or published

Hi there, 

I have added this CSS to my form

.form-all {

    border : solid #5C6F7B;

}

...and the border shows up in the design mode. But the border is missing when I click Preview or when published. Please could someone help?

Upon inspection, it turned out that this CSS rule was overridden, please use this custom CSS instead like this:

.form-all {
    border: solid #5C6F7B !important;
}

Please let us know if you need further assistance with the issue.