HTML, CSS and JS are inherent to all websites and represent the parts that clients interact with directly.
HTML is the code of the page, it is the language that includes tags , , and text. Once the code is written, you obtain a page on which you can find all our information, the website at this stage does not include a layout or UI design, it is a "barebones" website.
CSS is a language that will format the information int he HTML, it is the first graphic design stage, since we integrate all the elements of the brand's style at this point. At this stage in the website's development, it is attractive but does not yet have UX design that includes button ergonomics and style effects.
Javascript enables us to add effects to increase the dynamics of the website, particularly the buttons, menus, images / pictograms / purchase funnel, etc... It is the stage where UI design is developed.