Low-resolution icon appears blurry in HiDPI screens
The icon provided has a low resolution, and therefore appears blurry when viewed in HiDPI screens. This contrasts with the other, sharper icons.

As an alternative to using the icon, one can also use the unicode search character:
.ol3-geocoder-btn-search {
background-image: none;
}
.ol3-geocoder-btn-search:before {
content: '🔍';
font-size: 0.7em;
line-height: 0.8em;
}

Optionally, in case you prefer the old icon for non-HiDPI devices, this icon could be used only in HiDPI devices using media queries:
@media only screen and (-webkit-min-device-pixel-ratio: 1.3),
only screen and (-o-min-device-pixel-ratio: 13/10),
only screen and (min-resolution: 120dpi) {
.ol3-geocoder-btn-search {
background-image: none;
}
.ol3-geocoder-btn-search:before {
content: '🔍';
font-size: 0.7em;
line-height: 0.8em;
}
}
@jmgomezpoveda Sorry the delay, I'm right now in a hurry and ASAP will give it a closer look.
@jmgomezpoveda
Are you able to prepare a PR with your suggestions?
I am afraid this may not work with 2.4.0, due to the styling changes. Will need to analyse the impact to port it to 2.4.0.
Closed in v4.3.1 Icon replaced by unicode char