ArjhanToteck

you do have an invalid structure. You css style has double closing brackets. Chrome will automatically correct that
 
<style type="text/css"> table td{ /* border: #000 solid 1px; */ border-bottom: 1px solid #000; padding: 5px; } } /* <----- here is your issue */ </style>  

Please don't.
 
Longer, but less recommendable answer: Try Electron.
Also, stop randomly adding colors please.

I'm the friend Duckster was talking about. What you should do is assign a blank variable to the textbox where the characters are being typed. Then you can make another variable and assign the length of the first variable to the second variable. For example,
let text let characters Then you should add a variable called var1 and then make a loop that sets the value of characters to the length of text as long as var1 = 0, and within it an if statement that tests the amount of characters and alerts the user if there are more than 750 characters.
var var1 = 0 while(chracters < 751){ characters = text.length if(characters === 750|| characters > 750){ overMax() } } function overMax(){ \\ add alert lines here. } Depending on what you're file or application is, you can add the alert in the \\add alert lines here spot. This might work as the alert function;
function overMax(){ alert("You have 750 characters. You might want to save now to prevent losing some work in case of the program crashing.") }