I need my application run in multiple screen resolutions. Currently I have specified all the dimensions in percentage (%) instead of pixels (px) so that it will automatically re-size with the screen.
Which would be the more reliable unit of measurement for specifying dimensions on my webpage: Pixels (or EM) or Percentage
For Responsive Webdesign you really should be leveraging media queries
Personally I prefer pixels because they give me more control, and I can reliably know the exact dimensions of each element. With media queries you can also set new styles based on the screen resolution.
Percentages give you a nice responsive feel, but can be much more difficult to ensure you're layout is not junked by each level of resolution.
Both approaches are "reliable". However, if you are looking for auto-resizing, percentages is the way to go. If you do not want the elements to resize based on the size of the window, pixels would a better solution.
Percentage always applies to a percentage of the parent element, while pixels are always fixed. Percentages are more accessible especially on smaller monitors however you will run into problems with things line breaking at the wrong times and the like. For example, if you have a 50px image and 100px wide line of text, and you want the items on the same line, specify a 150px width, because if you specify a percent, they may appear right on your monitor but not others.
来源：https://stackoverflow.com/questions/9998850/css-percentage-widths-and-heights-and-resolution-problems