There are two ways to edit HTML in Bootstrap Studio. The first is by adding the "Custom Code" component to your page. The second is by converting a part of your page to HTML.
1. Writing HTML with "Custom Code"
"Custom Code" is a powerful component which gives you full control over its content. You can use it to quickly add HTML snippets to your pages.
To add the component to your design find it in the Components panel and drag and drop it to your page.
When you double click a custom code component (or when you right click it and choose "Edit Code"), it will open up a code editor in the bottom of the application window.
To edit your HTML file, just double click it. This will open our powerful code editor.
Here you have full control over the code. This editor supports most of the keyboard shortcuts you know and love from Sublime Text and other popular editors. When you hit "Apply" the changes you've made will be added to the page.
Note: HTML is sanitized and JS is disabled when Custom Code is displayed in Bootstrap Studio for security purposes. In Preview and when exporting, Custom Code is included in the page unmodified, exactly the way you've written it.