Code Block Hover Effect
A code snippet where the line under the pointer lights up with an accent edge and number, and a copy button slides in once you hover the block. Line numbers come from a CSS counter.
Also known as: code line highlight on hover, copy code button on hover, line numbers hover css.
.card { display: grid; gap: 1rem; transition: transform 0.3s;}HTML
<figure class="hfx-code-block-lines">
<button aria-label="Copy code"><svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><rect x="8" y="8" width="12" height="12" rx="2"/><path d="M16 8V5.5A1.5 1.5 0 0 0 14.5 4h-9A1.5 1.5 0 0 0 4 5.5v9A1.5 1.5 0 0 0 5.5 16H8"/></svg></button>
<pre><code><span><b>.card</b> {</span><span> <i>display</i>: <u>grid</u>;</span><span> <i>gap</i>: <u>1rem</u>;</span><span> <i>transition</i>: <u>transform 0.3s</u>;</span><span>}</span></code></pre>
</figure>CSS
.hfx-code-block-lines {
--c: var(--hfx-color, #3b82f6);
font-size: var(--hfx-size, 16px);
position: relative;
width: 18em;
margin: 0;
overflow: hidden;
border-radius: 0.8em;
background: #0f172a;
box-shadow: 0 0 0 1px color-mix(in srgb, var(--c) 30%, transparent);
color: #e2e8f0;
}
.hfx-code-block-lines pre {
margin: 0;
padding: 0.7em 0;
counter-reset: line;
font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
font-size: 0.85em;
line-height: 1.7;
}
.hfx-code-block-lines code > span {
display: block;
padding-right: 1em;
counter-increment: line;
white-space: pre;
transition: background-color 0.15s ease, box-shadow 0.15s ease;
}
.hfx-code-block-lines code > span::before {
content: counter(line);
display: inline-block;
width: 1.6em;
margin-right: 1.1em;
color: #475569;
text-align: right;
transition: color 0.15s ease;
}
.hfx-code-block-lines b { color: color-mix(in srgb, var(--c) 45%, #fff); font-weight: 600; }
.hfx-code-block-lines i { color: color-mix(in srgb, var(--c) 30%, #f0abfc); font-style: normal; }
.hfx-code-block-lines u { color: color-mix(in srgb, var(--c) 20%, #fcd34d); text-decoration: none; }
.hfx-code-block-lines code > span:hover {
background: color-mix(in srgb, var(--c) 20%, transparent);
box-shadow: inset 0.2em 0 0 var(--c);
}
.hfx-code-block-lines code > span:hover::before { color: color-mix(in srgb, var(--c) 50%, #fff); }
.hfx-code-block-lines > button {
position: absolute;
top: 0.55em;
right: 0.55em;
display: grid;
place-items: center;
width: 2em;
height: 2em;
padding: 0;
border: 1px solid rgba(255, 255, 255, 0.15);
border-radius: 0.45em;
background: rgba(255, 255, 255, 0.08);
color: #cbd5e1;
cursor: pointer;
opacity: 0;
transform: translateY(-0.35em);
transition: opacity 0.2s ease, transform 0.25s cubic-bezier(0.3, 0.7, 0.4, 1), background-color 0.15s ease;
}
.hfx-code-block-lines > button svg { width: 1em; height: 1em; }
.hfx-code-block-lines:is(:hover, :focus-within) > button {
opacity: 1;
transform: none;
}
.hfx-code-block-lines > button:is(:hover, :focus-visible) {
background: rgba(255, 255, 255, 0.18);
color: #fff;
}
@media (prefers-reduced-motion: reduce) {
.hfx-code-block-lines, .hfx-code-block-lines *, .hfx-code-block-lines::before, .hfx-code-block-lines::after, .hfx-code-block-lines *::before, .hfx-code-block-lines *::after {
animation-duration: 0.01ms !important;
animation-iteration-count: 1 !important;
transition-duration: 0.01ms !important;
}
}Customizing this snippet
- Color: set
--hfx-coloron the element or a parent. Currently previewing#3b82f6. - Base size: set
--hfx-size. Every other dimension is inem, so the whole thing scales together. Currently previewing16px. - Speed: change the duration on the
transitionoranimationshorthand. Staggered delays are relative, so they keep their rhythm. - Reduced motion: the rule at the end of the CSS turns the motion off for people who asked their OS for less of it. Keep it.