CSS：在不更改其容器大小的情况下加粗一些文本

body {
  font-family: segoe ui;
}

ul li {
  display: inline-block;
  border-left: 1px solid silver;
  padding: 5px
}

.textshadow :hover {
  text-shadow: 0px 0px 1px black;
}

.textshadow-alt :hover {
  text-shadow: 1px 0px 0px black;
}

.bold :hover {
  font-weight: bold;
}

<ul class="textshadow">
  <li>Item 1</li>
  <li>Item 2</li>
  <li>Item 3</li>
  <li><code>text-shadow: 0px 0px 1px black;</code></li>
</ul>

<ul class="textshadow-alt">
  <li>Item 1</li>
  <li>Item 2</li>
  <li>Item 3</li>
  <li><code>text-shadow: 1px 0px 0px black;</code></li>
</ul>

<ul class="bold">
  <li>Item 1</li>
  <li>Item 2</li>
  <li>Item 3</li>
  <li><code>font-weight: bold;</code></li>
</ul>

li             { color: #000; } /* set text color just in case */
.shadow0       { text-shadow: inherit; }
.shadow2       { text-shadow: -0.02ex 0 #000, 0.02ex 0 #000; }
.shadow4       { text-shadow: -0.04ex 0 #000, 0.04ex 0 #000; }
.shadow6       { text-shadow: -0.06ex 0 #000, 0.06ex 0 #000; }
.shadow8       { text-shadow: -0.08ex 0 #000, 0.08ex 0 #000; }
.bold          { font-weight: bold; }
.bolder        { font-weight: bolder; }
.after span        { display:inline-block; font-weight: bold; } /* workaholic… */
.after:hover span  { font-weight:normal; }
.after span::after { content: attr(title); font-weight: bold; display:block; 
                     height: 0; overflow: hidden; }
.ltrsp         { letter-spacing:0; font-weight:bold; } /* @cgTag */
li.ltrsp:hover { letter-spacing:0.0125ex; }
li:hover       { font-weight: normal!important; text-shadow: none!important; }

<li class="shadow0">MmmIii123 This line tests shadow0 (plain)</li>
<li class="shadow2">MmmIii123 This line tests shadow2 (0.02ex)</li>
<li class="shadow4">MmmIii123 This line tests shadow4 (0.04ex)</li>
<li class="shadow6">MmmIii123 This line tests shadow6 (0.06ex)</li>
<li class="shadow8">MmmIii123 This line tests shadow8 (0.08ex)</li>
<li class="after"><span title="MmmIii123 This line tests [title]"
                   >MmmIii123 This line tests [title]</span> (@workaholic…)</li>
<li class="ltrsp"  >MmmIii123 This line tests ltrsp (@cgTag)</li>
<li class="bold"   >MmmIii123 This line tests bold</li>
<li class="bolder" >MmmIii123 This line tests bolder</li>
<li class="shadow2 bold">MmmIii123 This line tests shadow2 (0.02ex) + bold</li>
<li class="shadow4 bold">MmmIii123 This line tests shadow4 (0.04ex) + bold</li>
<li class="shadow6 bold">MmmIii123 This line tests shadow6 (0.06ex) + bold</li>
<li class="shadow8 bold">MmmIii123 This line tests shadow8 (0.08ex) + bold</li>

/* checkbox and radiobutton */
label
{
    position: relative;
    display: inline-block;
    padding-left: 30px;
    line-height: 28px;
}

/* reserve space of bold text so that the container-size remains the same when the label text is set to bold when checked. */
label > input + b + i
{
    font-weight: bold;
    font-style: normal;
    visibility: hidden;
}

label > input:checked + b + i
{
    visibility: visible;
}

/* set title attribute of label > b */
label > input + b:after
{
    display: block;
    content: attr(title);
    font-weight: normal;
    position: absolute;
    left: 30px;
    top: -2px;
    visibility: visible;
}

label > input:checked + b:after
{
    display: none;
}

label > input[type="radio"],
label > input[type="checkbox"]
{
    position: absolute;
    visibility: hidden;
    left: 0px;
    margin: 0px;
    top: 50%;
    transform: translateY(-50%);
}

    label > input[type="radio"] + b,
    label > input[type="checkbox"]  + b
    {
        display: block;
        position: absolute;
        left: 0px;
        margin: 0px;
        top: 50%;
        transform: translateY(-50%);
        width: 24px;
        height: 24px;
        background-color: #00a1a6;
        border-radius: 3px;
    }

    label > input[type="radio"] + b
    {
        border-radius: 50%;
    }

    label > input:checked + b:before
    {
        display: inline-block;
        position: absolute;
        top: 50%;
        left: 50%;
        transform: translate(-50%, -50%) rotate(45deg);
        content: '';
        border-width: 0px 3px 3px 0px;
        border-style: solid;
        border-color: #fff;
        width: 4px;
        height: 8px;
        border-radius: 0px;
    }

    label > input[type="checkbox"]:checked + b:before
    {
        transform: translate(-50%, -60%) rotate(45deg);
    }

    label > input[type="radio"]:checked + b:before
    {
        border-width: 0px;
        border-radius: 50%;
        width: 8px;
        height: 8px;
    }

<label><input checked="checked" type="checkbox"/><b title="Male"></b><i>Male</i></label>
<label><input type="checkbox"/><b title="Female"></b><i>Female</i></label>