There is a frame with the calculation of the area. I just can’t figure out how to make the background of the frame change when making calculations.

<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <title>Фрейм 4. Выделение поля "сторона"</title> </head> <body style="background-color: #E4E4CB"> <H1>Вычисление площади</H1> <p><b>Выделите поле 'сторона'</b></p> <p style="font-family: Courier">Сторона: <input type="text" id="length" value="24"></p> <p style="font-family: Courier">Площадь: <input type="text" id="sqr"></p> <script> "use strict"; var elLength = document.getElementById("length"); var elSqr = document.getElementById("sqr"); elLength.onselect = function(e) { var result = Math.pow(parseFloat(elLength.value), 2) if (!isNaN(result)) { elSqr.value = result; } else { elSqr.value = ""; } } </script> </body> </html>

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