You can place all of your custom css definitions in yourjoomla/templates/yourtemplate/css folder if you create a custom.css or user.css file in this folder. Since this does not always work with every templates, then you can use a free plugin to load your custom css codes/style:
https://extensions.joomla.org/extension/add-custom-css/
This way you can reuse your 'special' div class styles in other articles too and you do not have to define div styles article by article...
And I really forgot to mention that you need to use for example CodeMirror editor in your Joomla and you can edit the articles in full html mode in that case, which you can set at Global configuration->Default Editor->Editor-CodeMirror . And that way together with the above styling solution or with inline styling you can create any kind of html pages/articles. (I am sorry for leaving out this important part from my answer earlier).