Hello, Steven Tay,
1,3. Please copy and paste the following CSS code to XStore >> Theme Options >> Theme Custom CSS >> Global CSS. After clearing the browser cache, the result should look like the image provided (https://postimg.cc/xNk4Pm7G). You can adjust the values in the code as needed.
.woocommerce-account .wcfmmp_become_vendor_link a {
font-size: 20px !important;
color: #fff !important;
}
.woocommerce-account .wcfmmp_become_vendor_link {
background-color: #000 !important;
border: 1px solid #000 !important;
border-radius: 20px !important;
padding-top: 5px !important;
padding-bottom: 5px !important;
text-align: center !important;
}
2. If you want to change that word or translate it, you have to change/translate it into the multivendor plugin language files which you are using on your site, you can use the loco translate the plugin to translate it.
We hope this helps.
Best Regards,
8Theme’s Team