Margin-top not working with <label>

问题

I'm trying to just nudge the email label and input down a little by assigning a class 'brtop' to the label.

.brtop just adds a top margin.

Doesn't seem to be doing anything, have I done something wrong?

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/*  ^^CSS_RESET^^ --- vv CSSforsite vv */

form{
	width:500px;
	padding:1.5em;
	overflow:hidden;
	border:1px solid red;
}
fieldset{
	float:left;
	border:none;
	margin-left:1em;
}

.brtop{
margin-top:5px;
}

input{
}

<form name="messageform">
		<fieldset>
			<label for="username" >Name:</label><br/>
			<input type="text" name="username"/><br/>
			<label for="email"class="brtop">Email:</label><br/>
			<input type="text" name="email"/>
		</fieldset>
		<fieldset>
			<label>Message:</label><br/>
			<textarea name="message" cols="20" rows="4"></textarea>
		</fieldset>		
	</form>

回答1:

Add display:inline-block to your brtop rule.

.brtop {
    margin-top:5px;
    display:inline-block;
}

/* html5doctor.com Reset v1.6.1 - http://cssreset.com */

html,
body,
div,
span,
object,
iframe,
h1,
h2,
h3,
h4,
h5,
h6,
p,
blockquote,
pre,
abbr,
address,
cite,
code,
del,
dfn,
em,
img,
ins,
kbd,
q,
samp,
small,
strong,
sub,
sup,
var,
b,
i,
dl,
dt,
dd,
ol,
ul,
li,
fieldset,
form,
label,
legend,
table,
caption,
tbody,
tfoot,
thead,
tr,
th,
td,
article,
aside,
canvas,
details,
figcaption,
figure,
footer,
header,
hgroup,
menu,
nav,
section,
summary,
time,
mark,
audio,
video {
  margin: 0;
  padding: 0;
  border: 0;
  outline: 0;
  font-size: 100%;
  vertical-align: baseline;
  background: transparent
}

body {
  line-height: 1
}

article,
aside,
details,
figcaption,
figure,
footer,
header,
hgroup,
menu,
nav,
section {
  display: block
}

nav ul {
  list-style: none
}

blockquote,
q {
  quotes: none
}

blockquote:before,
blockquote:after,
q:before,
q:after {
  content: none
}

a {
  margin: 0;
  padding: 0;
  font-size: 100%;
  vertical-align: baseline;
  background: transparent
}

ins {
  background-color: #ff9;
  color: #000;
  text-decoration: none
}

mark {
  background-color: #ff9;
  color: #000;
  font-style: italic;
  font-weight: bold
}

del {
  text-decoration: line-through
}

abbr[title],
dfn[title] {
  border-bottom: 1px dotted;
  cursor: help
}

table {
  border-collapse: collapse;
  border-spacing: 0
}

hr {
  display: block;
  height: 1px;
  border: 0;
  border-top: 1px solid #ccc;
  margin: 1em 0;
  padding: 0
}

input,
select {
  vertical-align: middle
}


/*  ^^CSS_RESET^^ --- vv CSSforsite vv */

form {
  width: 500px;
  padding: 1.5em;
  overflow: hidden;
  border: 1px solid red;
}

fieldset {
  float: left;
  border: none;
  margin-left: 1em;
}

.brtop {
  margin-top: 5px;
  display: inline-block;
}

input {}

<form name="messageform">
  <fieldset>
    <label for="username">Name:</label>
    <br/>
    <input type="text" name="username" />
    <br/>
    <label for="email" class="brtop">Email:</label>
    <br/>
    <input type="text" name="email" />
  </fieldset>
  <fieldset>
    <label>Message:</label>
    <br/>
    <textarea name="message" cols="20" rows="4"></textarea>
  </fieldset>
</form>

Since your label is displaying as an inline element, the top margin won't have any effect.

Margin properties specify the width of the margin area of a box. The 'margin' shorthand property sets the margin for all four sides while the other margin properties only set their respective side. These properties apply to all elements, but vertical margins will not have any effect on non-replaced inline elements. - W3

回答2:

<label> is display: inline. If you add display: inline-block to .brtop it will respect the margin.

来源：https://stackoverflow.com/questions/15929141/margin-top-not-working-with-label