Workflow for a new style

Say I want to define a new custom style. (For example a style I call “alert text”, with red background and white text). For example,

===Alert Text===

So, text inside triple equal signs will be converted into such text. (Similar to code text turns into code formatting.) And say I want to assign a certain keyboard shortcut to enclose the selected text. (Like CTRL-B for Bold). What would be a suggested workflow for all of this?