The @charset CSS at-rule specifies the character encoding used in the style sheet.
Some say it is not important anymore because a browser user agent can easily deduce the character encoding, but I have seen on rare occasions where omitting it has produced unsupported issues on CSS properties on older browsers (i.e. :before).
If you want a images on your website (especially image buttons with text) to look sharp on retina displays (iPhone 4/5/6, iPad Mini, iPad 3/4), you can create a separate image with double the pixel density.
Which only means creating a version of your images at twice the size, so a 200 x 200px image would become 400x400px. These super sized images are then displayed in the original image size dimensions, which helps create that smooth and crisp appearance on high pixel density screens.
Then just create a media query for only displays that have a pixel ratio of 2:
The HTML5 placeholder attribute lets you provide a short hint that helps people enter the right information into a form field.
The hint might be an example of the required information, or a description of the expected format. The placeholder hint or description is displayed inside the empty form field, and is removed as soon as the field is given focus.
<input name="first_name"placeholder="Your first name..."type="text">
The trouble is that once the field is given focus and the placeholder text disappears, there’s nothing left to explain what kind of information should be entered. It’s also inconvenient for keyboard users. Instead of tabbing onto a field and reading the label, they need to look ahead to read the placeholder before moving focus to the field itself