@Nam-Hai
Posted
First of all try to get as close as possible to the originale design. For exemple here the buttons need to have round edges. The bill and nb of people inputs were not suppose to have the "number" type. You could have add the error text in red when you put 0 person, as shown in the orignal design.
You also kind of cheated on the javascript part as you changed the reset button with a calculate button, which make the javascript fairly simpler.
If you stoped coding for a long time i'd suggest you to start with simpler design and quickier design to get back on track and have solide basis on the HTML/CSS, and to don't have to bother at first with the Js.