It is recommend that you make a copy of an existing theme and edit it. In order to be able to edit the theme and see changes without restarting the keycloak server you need to edit the standalone.xml file on your keycloak server to disable caching.
located here
./standalone/configuration/standalone.xml
Make the following changes to standalone.
<theme>
<staticMaxAge>-1</staticMaxAge>
<cacheThemes>false</cacheThemes>
<cacheTemplates>false</cacheTemplates>
...
</theme>
To change the title for your login and register user screen you can edit the CSS located at
./bootstrapTheme/login/resources/css/styles.css
Make changes here to change the title
To change your background colour or set a background image
.login-pf body {
background: #f5f6fa;
/*background-image: url('../img/bkgrnd.jpg');*/
background-size: cover;
}
To change the login and register button
/*button*/
#kc-form-buttons > input {
background-color: #0168fa !important;
border-color: #0168fa !important;
border-radius: 0.25rem;
background-image: none;
}
More information see Keycloak Themes documentation here