On many websites that allow users to create an account and then log in to it on subsequent dates, there is a standard feature in which the user may input their user name and password into separate form fields arranged on a pop-up element. Underneath these fields will usually be a prominently displayed button that allows the user to sign in to the account matching those fields' contents.
Oftentimes, this form field will feature an additional option that lets users attempt to retrieve either their user name or their password if they had forgotten either of these pieces of identifying information since the last time those were used to log in. Since this is an option that should rarely come into play for the average user, it is usually present on the form as a much smaller clickable element than the "sign in" or "log in" button.
This shows the significance that the aesthetic presentation of buttons can have in making a website's sign-in feature easily understood at a glance by the user. Because of the codification of web design standards over the decades, users are accustomed to button-shaped interactive features resulting in special actions taking place on the page itself. Underlined links, on the other hand, are commonly understood to exist merely for the sake of transporting users to different URLs.
At times, websites will also include the option of letting a new user create a new account on the same web pop-up as the option of signing in to one. Websites generally have to decide for themselves whether it is better to conveniently have both options accessible from the same pop-up or to avoid potential mistaken button clicks by having different pop-ups for each function. If both functions are on the same pop-up, then the chance that users will click on the wrong button will be needlessly high if the buttons share a similar shape and are competing for the user's attention. In the worst-case scenario, a user may accidentally create an unwanted extra account, so the account-creation button should generally be the smaller of the two. For more information click here https://i.redd.it/jo8ovkmukch61.jpg.