Class Range and Class Sheet have methods you can use to pick the row that the cell is in. This is similar to the technique used in this answer.
SpreadsheetApp.getActiveSheet().getRange(SpreadsheetApp.getActiveRange().getRow(),1,1,SpreadsheetApp.getActiveSheet().getLastColumn()).setBackgroundRGB(224, 102, 102);
This does the same thing, broken down into easier-to-read lines:
var sheet = SpreadsheetApp.getActiveSheet();
var activeRange = SpreadsheetApp.getActiveRange();
var changeRange = sheet.getRange(activeRange.getRow(),1,1,sheet.getLastColumn());
changeRange.setBackgroundRGB(224, 102, 102);