Div height not zero when collapsible panel closed - html

Question

I have the following panel that shows it's contents when the label for the hidden checkbox is clicked and hides them when clicked again.
.collapse-panel {
margin-bottom: 20px;
border-bottom: 2px solid darkblue;
}
.collapse-panel > label {
display: block;
position: relative;
top: -5px;
height: 2px;
}
.collapse-panel > input {
display: none;
}
.collapse-panel > label:before {
content: 'vvv';
float: left;
padding: 2px;
border: 1px solid darkblue;
border-radius: 5px;
font-family: "Lucida Console", Monaco, monospace;
font-size: 8pt;
font-weight: bold;
color: deepskyblue;
background-color: white;
cursor: pointer;
}
.collapse-panel div.collapse-panel-content {
display: inline-block;
height: 0;
margin: 0;
overflow: hidden;
white-space: nowrap;
transition-property: all;
transition-duration: 1.0s;
transition-timing-function: ease-in-out;
}
.collapse-panel > input:checked ~ div.collapse-panel-content {
height: 25px;
}
.collapse-panel > input:checked ~ label:before {
content: '^^^';
padding-top: 4px;
padding-bottom: 0;
font-size: 9pt;
}
div.collapse-panel-content > * {
display: inline-block;
float: right;
max-width: 30px;
margin: 5px;
}
<div class="collapse-panel">
<input type="checkbox" name="" id="collapse_panel_checkbox">
<div class="collapse-panel-content">
<div style="height: 20px; width: 20px; background-color: red;">
</div>
<div style="height: 20px; width: 20px; background-color: green;">
</div>
<div style="height: 20px; width: 20px; background-color: blue;">
</div>
</div>
<label for="collapse_panel_checkbox"></label>
</div>
However, when closed, the panel height is not zero; it is 20px.
How can I refactor to have the panel height drop to zero when collapsed?

Answer 1

Set font-size:0; to .collapse-panel, because it's containing inline-block elements, Inline boxes inherit inheritable properties from their block parent element, and creates space/margin. font-size:0; will remove those space.
.collapse-panel {
margin-bottom: 20px;
border-bottom: 2px solid darkblue;
font-size:0;
}
.collapse-panel > label {
display: block;
position: relative;
top: -5px;
height: 2px;
}
.collapse-panel > input {
display: none;
}
.collapse-panel > label:before {
content: 'vvv';
float: left;
padding: 2px;
border: 1px solid darkblue;
border-radius: 5px;
font-family: "Lucida Console", Monaco, monospace;
font-size: 8pt;
font-weight: bold;
color: deepskyblue;
background-color: white;
cursor: pointer;
}
.collapse-panel div.collapse-panel-content {
display: inline-block;
height: 0;
margin: 0;
overflow: hidden;
white-space: nowrap;
transition-property: all;
transition-duration: 1.0s;
transition-timing-function: ease-in-out;
}
.collapse-panel > input:checked ~ div.collapse-panel-content {
height: 25px;
}
.collapse-panel > input:checked ~ label:before {
content: '^^^';
padding-top: 4px;
padding-bottom: 0;
font-size: 9pt;
}
div.collapse-panel-content > * {
display: inline-block;
float: right;
max-width: 30px;
margin: 5px;
}
<div class="collapse-panel">
<input type="checkbox" name="" id="collapse_panel_checkbox">
<div class="collapse-panel-content">
<div style="height: 20px; width: 20px; background-color: red;">
</div>
<div style="height: 20px; width: 20px; background-color: green;">
</div>
<div style="height: 20px; width: 20px; background-color: blue;">
</div>
</div>
<label for="collapse_panel_checkbox"></label>
</div>
Source

Answer 2

You can make the height of the panel like this way: If I got your question correct.
.collapse-panel > input ~ div.collapse-panel-content {
height: 0;
}
.collapse-panel {
margin-bottom: 20px;
border-bottom: 2px solid darkblue;
}
.collapse-panel > label {
display: block;
position: relative;
top: -5px;
height: 2px;
}
.collapse-panel > input {
display: none;
}
.collapse-panel > label:before {
content: 'vvv';
float: left;
padding: 2px;
border: 1px solid darkblue;
border-radius: 5px;
font-family: "Lucida Console", Monaco, monospace;
font-size: 8pt;
font-weight: bold;
color: deepskyblue;
background-color: white;
cursor: pointer;
}
.collapse-panel div.collapse-panel-content {
display: inline-block;
height: 0;
margin: 0;
overflow: hidden;
white-space: nowrap;
transition-property: all;
transition-duration: 1.0s;
transition-timing-function: ease-in-out;
}
.collapse-panel > input:checked ~ div.collapse-panel-content {
height: 25px;
}
.collapse-panel > input ~ div.collapse-panel-content {
height: 0;
}
.collapse-panel > input:checked ~ label:before {
content: '^^^';
padding-top: 4px;
padding-bottom: 0;
font-size: 9pt;
}
div.collapse-panel-content > * {
display: inline-block;
float: right;
max-width: 30px;
margin: 5px;
}
<div class="collapse-panel">
<input type="checkbox" name="" id="collapse_panel_checkbox">
<div class="collapse-panel-content">
<div style="height: 20px; width: 20px; background-color: red;">
</div>
<div style="height: 20px; width: 20px; background-color: green;">
</div>
<div style="height: 20px; width: 20px; background-color: blue;">
</div>
</div>
<label for="collapse_panel_checkbox"></label>
</div>