In web development, padding refers to the space between an element's content and its border. Padding can be specified using CSS (Cascading Style Sheets) and is often used to create a visual buffer between an element's content and its border. Padding values can be specified using different units of measurement such as pixels, ems or percentages.

Here's an example in CSS:

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div {
  padding: 20px; /* sets equal padding on all sides of the element */
}

This would add 20 pixels of padding to all sides of the div element, creating space between the element's content and its border.

I'm assuming you mean changing the dimensions of an element from other units to pixels. To do this, you can use CSS.

Let's say your element has a width of 50% and a margin of 1em. To convert these to pixels, you'll need to know the width of the parent element and the font-size of your document. Once you have those values, you can calculate the width and margin in pixels using the formula:

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value in pixels = (value in other unit) * (parent width in pixels) / 100

For example, let's say the parent element has a width of 800px and the font-size is 16px. To convert the width of the element to pixels, you would do:

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width in pixels = 50% * 800 / 100 = 400px

To convert the margin to pixels, you would need to know the value of 1em in pixels (which is equal to the font-size). Let's say 1em is equal to 16px:

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margin in pixels = 1em * 16px = 16px

So your updated CSS would be:

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element {
  width: 400px;
  margin: 16px;
}

Remember to adjust the values based on your specific case.

The background-position property sets the starting position of a background image. It can take up to two values which represent the horizontal and vertical positions respectively. The background-position values can be either pixels (px), percentages (%) or pre-defined keywords like top, bottom, center, left, right.

For example, to set the background image position to be centered horizontally and aligned to the top vertically, you would use:

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background-position: center top;

You can read more about the usage of background-position on MDN web docs.

em and px are units of measurement used to specify the size of elements on a webpage.

px stands for pixels, and it is a fixed-size unit of measurement that does not change with resizing.

em stands for "em"phasis, and it is a relative unit of measurement that adjusts based on the font-size set for a parent element.

For example, if you set the font-size of a parent element to 16px and you set the font-size of a child element to 1em, the child element will have a font size of 16px because 1em is equal to the font-size of the parent element.

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p {
  font-size: 16px;
}

span {
  font-size: 0.8em;
}

In this example, the font size of the span element will be 80% of the font size of the p element because 0.8em is equal to 80% of the font-size of the parent element.

You can learn more about em and px units here.

With CSS you can change the size of your image using the width and height properties. You can specify the size in either percentages or pixels.

For example:

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img {
    width: 70%;
    height: 70%;
} 

This would set the width and height of your image to 70% of the original size.

Alternatively, if you want to set the size in pixels instead, you would use:

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img {
    width: 350px;
    height: 350px;
} 

This would set the width and height of your image to 350 pixels each.

Vector graphics are composed of lines, shapes and text that are mathematically generated and stored in a computer as mathematical formulas. These graphics don't lose detail when they are resized and can be edited simply by moving points and lines. Vector graphics are saved as scalable user defined files such as .svg, .eps, and .ai.

Raster graphics are composed of pixels, or small square dots of color. When the resolution of raster graphics increase the amount of pixels increases and the file size grows. Raster graphics cannot be scaled or edited after they are created and are saved as .jpg, .tiff, and .png.