BlueGriffon - WYSIWYG Web Content Editor
Speaking of HTML 5 elements, BlueGriffon allows you to directly embed HTML 5 audio or video elements.
The builtin Style Properties panel offers controls for all the CSS properties and values Gecko implements. The usual suspects from CSS 2 but also 2D Transforms, 3D Transforms, Transitions, Shadows, Linear and Radial Gradients, Repeating Gradients, Border Images, Columns, Flex Box Model, and more
BlueGriffon includes (with permission) the popular SVG editor SVG Edit and you can then draw vectorial graphics from within BlueGriffon to embed them into your documents.
In ubuntu set the permission of the installable you downloaded "Allow executing file as program" and launch. Right Click Install File - Permissions - check "Allow Executable .." and then double-click.