Thanks for the really useful feedback.
I am using Contact Forms 7.
I have installed some of the custom skins found here: https://themeover.com/plugin-styles/
I have installed Microloader in order to do this.
The skins work fine and look good (as mentioned) however, do not seem to work on any forms that have dropdown menus. Specifically, clicking the dropdown menu when a skin is applied does nothing – no options show up.
At this stage, I have uninstalled these themes/skins and have used CSS to style my form because it was breaking forms that are crucial to a client.
I cannot link you an example as I cannot afford to have my forms by live and broken.
I hope this is enough information.