select2 height code example

Example 1: .select2-selection__arrow { height: 34px !important; }

.select2-selection__rendered {
    line-height: 31px !important;
}
.select2-container .select2-selection--single {
    height: 35px !important;
}
.select2-selection__arrow {
    height: 34px !important;
}

Example 2: select2 full width

<select class="js-example-responsive" style="width: 50%"></select>
<select class="js-example-responsive" multiple="multiple" style="width: 75%"></select>

Example 3: select2 increase height

.select2-selection__rendered {
    line-height: 35px !important;
}
.select2-container .select2-selection--single {
    height: 35px !important;
}
.select2-selection__arrow {
    height: 35px !important;
}