Changing header colors on css code

Changing header colors on css code, how do I do?
" I would like to switch from # 25262b to #FFFFFF "
can you help me?

Hey there,

I hope you are well today and thank you for your question.

You can try achieving this by adding the following CSS code in the Custom CSS option of your theme on the below path.

Admin Area -> Appearance -> Customize -> Additional CSS

/*head background color white text black*/
.site-header {
    background: #fff;
    padding-top: 15px;
}
.sf-menu > li > a, .sf-menu > li.dropdown > a{
  color:black;
}
.top-header-bar-container {
    width: 100%;
    background: #fff;
    color: #000;
}
.top-header-bar-container a{
  color:#000;
}

Best regards,
Support.