# Migrating Legacy Applications to CSS

DevFeed: [Migrating Legacy Applications to CSS](<https://devfeed.tech/articles/migrating-legacy-applications-to-css-19371.md>)

Original publisher: [Read original article](<https://www.codenameone.com/blog/migrating-legacy-applications-to-css/>)

Author: Steve Hannah

Published: 2020-02-13T00:00:00Z

Content type: tutorial

Language: en

Sources: [CodeName One](<https://devfeed.tech/sources/codename-one.md>)

Topics: [CSS](<https://devfeed.tech/topics/css.md>), [App](<https://devfeed.tech/topics/app.md>), [GUI](<https://devfeed.tech/topics/gui.md>)

Tags: [applications](<https://devfeed.tech/tags/applications.md>), [css](<https://devfeed.tech/tags/css.md>), [customization](<https://devfeed.tech/tags/customization.md>), [designer](<https://devfeed.tech/tags/designer.md>), [gui](<https://devfeed.tech/tags/gui.md>), [legacy](<https://devfeed.tech/tags/legacy.md>)

## AI overview

This tutorial explains how to add CSS support to a legacy Codename One application that uses a designer-managed theme, while preserving the existing theme resources and GUI designs.

## Source excerpt

If you have an existing Codename One app that uses the designer for its theme, then you may have been reluctant to try to migrate it to CSS. Codename One projects are assumed to be using either CSS or the designer for their themes. But not both at the same time. When an app has CSS enabled, it compiles the css/theme.css to src/theme.res when the app is built, and it is kept in sync when changes are made to the theme.css file. Changes that you make manually to the theme.res file, would be lost the next time it synchronizes with the theme.css file. This doesn't jive with legacy projects where you have customized the theme.res using the designer.