UI Frameworks need more time to learn than just using raw HTML and CSS, but it will save more time and improve the overall quality. Using a UI framework in HTML will save a lot of time to adjust style sheets, and it is easy to implement elements that require Javascript, such as dropdown. As pages and functions become complex, the difficulty of using only raw HTML and CSS will easily increase, and the page will look messy. Using UI frameworks such as Semantic UI can easily reduce differences, and create beautiful and responsive layout pages.
The reward of learning UI Frameworks is greater than the time needed. Especially maintain websites that require constant use of HTML and CSS. UI framework helps developers easily change page layout, and add or remove features. Removing or adding a section on the page can be difficult to use only raw HTML and CSS (to easily accomplish the task by using the UI Framework), it is difficult because it may require the developer to adjust the entire style sheet, which may frustrate the developer. Therefore, it is very important to spend time learning UI frameworks, because it can save a lot of time and reduce the chance of feeling frustrated by maintaining messy code.
The UI framework has many software engineering advantages, the most important of which is the ability to develop quickly and save time for project development. Then, the developer can improve the project based on user feedback, such as adding, deleting, changing features or layout. In addition, when encountering problems using popular UI frameworks, other developers may have encountered problems before. Therefore, there is a great opportunity to find a solution online. Moreover, the UI framework can be similar to some coding standard, which helps to make the code clean for other programmers to read.