insert-logo.html

<style>
.logo-inra {
  background-image: url(images/logos/Logo-INRAE_Transparent.png);
  background-size: contain;
  background-repeat: no-repeat;
  position: fixed;
  bottom: -4em;
  width: 53px;
  height: 110px;
  z-index: 0;
  margin-bottom: -10px;
  left:25em;
}

.logo-migale {
  background-image: url(images/logos/migale-orange.png);
  background-size: contain;
  background-repeat: no-repeat;
  position: fixed;
  bottom: -4em;
  width: 85px;
  left: 7em;
  height: 116px;
  z-index: 0;
  margin-bottom: -10px;
  left:28em;
}

.logo-univ {
  background-image: url(../images/logo_UParis.png);
  background-size: contain;
  background-repeat: no-repeat;
  position: fixed;
  width: 205px;
  left: 7em;
  height: 60px;
  z-index: 0;
  left: 20em;
}

.logo-ifb {
  background-image: url(../images/logo-ifb_small.png);
  background-size: contain;
  background-repeat: no-repeat;
  position: fixed;
  width: 118px;
  left: 7em;
  height: 100%;
  z-index: 0;
  left: 34em;
}

.logo-inrae {
  background-image: url(../images/inrae.png);
  background-size: contain;
  background-repeat: no-repeat;
  position: fixed;
  width: 118px;
  left: 7em;
  height: 100%;
  z-index: 0;
  left: 16em;
}

.logo-migale {
  background-image: url(../images/migale-orange.png);
  background-size: contain;
  background-repeat: no-repeat;
  position: fixed;
  width: 118px;
  left: 7em;
  height: 100%;
  z-index: 0;
  left: 18em;
}

</style>

<script>
document
  .querySelectorAll(
    '.remark-slide-content' +
    '.title-slide' +
    // add additional classes to exclude here, e.g.
    // ':not(.inverse)' +
    ':not(.hide-logo)'
  )
  .forEach(el => {
    //el.innerHTML += '<div class="logo-inra"></div>';
    //el.innerHTML += '<div class="logo-migale"></div>';
    el.innerHTML += '<p style="text-align: center;"> \
    <img src="../images/logo-ifb_small.png" height="60px"></img> \
    <img src="../images/logo_UParis.png" height="60px"></img></p>';
    el.innerHTML += '<p style="text-align: center;"><img src="../images/migale-orange.png" height="40px"></img> \
    <img src="../images/inrae.png" height="35px"></img></p><p style="text-align: center;"><img src="../images/licence.png" height="40px"></img></p>';
  });
</script>