Sites traditionally have single custom fields in which people chuck all their content into. It can also be tricky for the people entering the content into the CMS to use and struggle with code. This is not the best way forward.
If you think of responsive images, that should be a single field in which the images html can be changed. If you have embedded all this content into single fields then you would have to do something really clever but more likely go through each entry and manually change the mark up.
Meet EE Blocks and Content Elements
Luckily there are 2 relatively new add-ons which can help us out. The first is EE Blocks. This is the more expensive of the two at $99 but it does a lot more than the second option - Content Elements which is $39.
Gives complete freedom to your content. You control every part of the markup and with as many custom sections as you may need. You have full control over the markup.
Once set up, the site editor can then add, reorder and edit as many of these blocks as you need, whilst having complete control over the outputted code. Edits don’t need to know any html as it’s all done in the control panel.
Tweet’s can also be added with the Media Embed add-on
Content Elements allows for pre defined sections / media to be added. You can add, headings, code output, galleries, tables and more. Whilst you cannot construct your own types of content these predefined types may be all you need. At less than half the price Content Elements more than has it’s uses.