<form class="csb-side" role="search">
  <label class="csb-sr" for="csb-side-i">Search</label>
  <input id="csb-side-i" type="search" name="q" placeholder="Search..." />
</form>

.csb-side {
  position: relative; display: inline-block;
}
.csb-side input {
  width: 240px; padding: 11px 14px 11px 18px;
  background: #1a1a28;
  border: 1px solid rgba(255,255,255,0.08);
  border-radius: 0 8px 8px 0;
  border-left: 3px solid #2a2a3e;
  color: #f0eeff; font: 500 14px/1 system-ui, sans-serif;
  outline: none;
  transition: border-left-color 0.25s;
}
.csb-side input::placeholder { color: #b8b6d4; }
.csb-side input:focus { border-left-color: #2ecc8a; }

.csb-sr {
  position: absolute !important;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}